Ibni Abidin (rahmat ullahi 'alaih) says in the chapter about the oath, in the third volume, and at he end of the chapter about the fast, in the second volume of the explanation of Durr- ul-mukhtar:

Nazr, that is, adaq (vow), is a kind of worship. Nazr is performed only for Allahu ta'ala. It is not performed for men. There are two kinds of vowing: absolute nazr, and conditional nazr.

1 - Absolute nazr is, for example, to say, "I shall fast for one year for the sake of Allahu ta'ala." It is not dependent upon a condition. It becomes wajib to fulfill it, even if one did not mean it while saying it or it slipped out inadvertently during a conversation. For, in matters of talaq (divorce) and nazr, uttering without an intention or thought is like uttering seriously and intentionally. In fact, if one inadvertently says, "...to fast for a month..," instead of saying, "Let it be a debt upon me to fast for a day for Allahu ta'ala," it becomes necessary for one to fast for a month.

Nazr is a worship. For, namaz, fasting, going on hajj, manumitting a slave, and other kinds of worship can be vowed. The Sharia commands the fulfillment of the nazr. It is sinful not to fulfill it. Nazr is like taking an oath. If a person says, "Let it be my nazr," without naming the thing vowed and without intention, it becomes necessary for him to pay the kaffarat prescribed for an oath. If a person says, "I will fast for Allah's sake," without mentioning the number of days of the fast and without intending for anything, or if he intends only for a nazr without thinking of whether or not it is an oath, or if he intends both for a nazr and for an oath, his fasting becomes a nazr, and he fasts three days. If he intends not for a nazr but for an oath while saying it, it becomes an oath. If he breaks his fast it becomes necessary for him to pay the kaffarat (penalty) prescribed for an oath. If he intends both for a nazr and for an oath, or only for an oath, the fasting becomes both an oath and a nazr. If he breaks the fast, both qada and the kaffarat for breaking an oath become necessary.

The thing vowed has to be like a kind of worship which is fard or wajib and has to be a worship by itself. For example, making an ablution or shrouding the dead, which are not acts of worship by themselves, cannot be a nazr. Visiting the ill, carrying the dead Muslims to their graves, making a ghusl, entering mosques, holding the Qur'an, calling the adhan, building schools, building mosques are worships, too. But none of them is a worship by itself. They cannot be vowed. The fard or wajib which the vowed thing has to be like does not have to be a worship by itself. For example, it is permissible to vow donating something to a pious foundation. For, donating something to a pious foundation is like building a mosque for Muslims. Building a mosque is not a worship by itself, but its donation to a pious foundation is a worship by itself. For example, making an ablution is not a worship by itself, but it is a condition (to be fulfilled for the acceptability) of namaz, which is a worship by itself. Likewise, shrouding a dead Muslim is a condition for the acceptability of the namaz of janaza. The satr-i-awrat of the dead is a condition of the namaz of janaza.

One has to fulfill the absolute nazr immediately, even if one is poor. If the state of death is felt before one has fulfilled it, one has to add fulfillment of kaffarat to one's will. It is also permissible to delay it without a good excuse. When fulfilling the nazr, one does not have to fulfill also the things which one has designated to do. For example, if one has vowed to give a certain amount of money to a particular poor person at a certain place and time, or to perform the namaz at a certain place, one does not have to observe these appointments. But one cannot change the vowed amount. And if one vows to give gold coins to a certain poor person at a certain place for Allah's sake, one will have to give them to that particular poor person. For, one's not appointing the gold coins or property one is going to give shows that one wants to appoint the poor person.

2 - Conditional vow. When the condition one has desired occurs one has to fulfill the nazr. [It is written in Fatawa-i-khayriyya that it is permissible to pay the kaffarat prescribed for an oath instead of fulfilling the nazr. It is written at the end of the chapter about fasting in the marginal notes titled Imdad by Tahtawi (rahmatullahi ta'ala 'alaih), "It is deduced from ayats and hadiths that nazr is permissible. If one has made the nazr depend upon the occurrence of a condition one desires, one will have to fulfill the nazr when the condition one has stipulated occurs. If one has stipulated a condition one does not desire to occur, when the condition one does not desire occurs one fulfills the nazr if one likes, if the nazr is hajj, fasting, alms, or supererogatory namaz. If one does not want to fulfill the nazr of this kind, one may pay the kaffarat for an oath instead. For example, if one says, "May it be my nazr to give a hundred pounds as alms for Allah's sake if I ever speak to Ali again," and then speaks to Ali, he has a choice between giving the alms or paying the kaffarat prescribed for an oath. But if one has said, "May my wife be divorced...," one will have divorced one's wife when one speaks to Ali, and it will not be permissible to pay the kaffarat for an oath. It is not permissible to fulfill the nazr dependent upon a condition before the condition occurs. For example, if one has said, "May it be my nazr to give so and so much money as alms for Allah's sake and present the thawab for it to the soul of Hadrat Sayyid Ahmad Badawi if my such and such ill relative recovers," it is not permissible to fulfill the nazr before the ill person recovers. One has to fulfill it after the ill person recovers. Like in the former case, when fulfilling the dependent nazr it is not necessary to fulfill the appointments one has made as to time, identity of the poor person, number of the poor people, or kind of money. The dependent nazr shouldn't be fulfilled in return for the occurrence of the stipulated condition. It should be fulfilled as thanks to Allahu ta'ala. It is like making the sajda (prostration) of thanks to Him].

Necessity of the fulfillment of nazr is declared in Qur'an al-karim and in hadiths, and there is ijma'i-umma on this. The twenty-ninth ayat of Hajj Sura declares: "They must fulfill their vows!" It is, therefore, wajib to fulfill the nazr. Some ('ulama) said that it is fard.

Fasting, salat [namaz], alms, i'tikaf, manumiting slaves, and hajj, - even by walking -, can be vowed. For, each of these is a worship by itself and is like either a fard or a wajib. For example, it is fard to manumit a slave for the kaffarat of fasting. Going on hajj by walking is fard for those Meccans who can. The worship here is not walking, but it is the hajj. And i'tikaf is like the sitting posture in the last rakat of namaz. As for waqf (donation to a pious foundation), it is fard for the state to build a mosque for Muslims in every city by using the money of the Baytulmal. If the state does not build it, it becomes fard upon Muslims.

When the nazrs of i'tikaf, hajj, salat, fasting, alms are not dependent, it is permissible to fulfill them without observing the appointments as to time, place, identity of the poor, and kind of money. For example, if one vows to give certain silver coins to a certain poor person in Mecca, on, let us say, Friday, it is permissible for one to give other silver coins to another person at some other place and time instead. It is permissible to perform the vowed hajj, salat, i'tikaf, or fasting before the time appointed during the vow. But it will not be acceptable if the number of days is one day less (than the vowed number). The dependent nazr cannot be fulfilled before the condition it depends on occurs. One can still make changes as to the poor person (to be given the alms), place, and kind of money.

If a person who has made it his nazr to fast every day during the month of Rajab becomes ill and cannot fulfill it, he will have to make qada of his fastings later, as with Ramadan.

If something unlike any fard or wajib is vowed, it is not necessary to fulfill it. The type of worship it is like has to be a fard-i-ayn. It is not necessary to fulfill the nazr which is like a fard-i-kifaya. An example of this is visiting a sick person. Entering a mosque cannot be vowed, though it is fard to enter the Majid-i-haram for tawaf (visiting) or to enter a mosque after the imam for Friday prayer. For, entering a mosque is not a worship by itself, but it is a part of a worship. Though it is fard to help one's needy parents, visiting one's parents cannot be vowed because it is not a worship by itself.

To sum up, when something is vowed its fulfillment is necessary if it has five conditions:

I - It has to belong to the class of a fard-i-ayn or wajib.

II - It has to be an act of worship by itself.

III - It shouldn't be a sin in itself. It is permissible to vow to fast on the 'Iyd day of qurban. For, fasting is not a sin in itself. In this case one will have to fast some other day. Vowing something which is haram becomes an oath. It is sinful to fulfill it. For example, when one vows to kill so and so, one does not kill so and so, but pays the kaffarat for an oath, instead.

IV - It is not sahih to vow to do something which is already fard for one to do. For example, hajj is already fard for a rich person who vows to become hajji. To vow to become a hajji is to inform that one is going to make the hajj that is fard. For, he who makes a supererogatory hajj cannot become a hajji. Because it is not sahih to vow the hajj which is fard, in this case it is fard for the rich person to make hajj only once. It is not necessary for him to go again for the fulfillment of his vow.

If a rich person vows to kill a sheep as a qurban on one of the days of the 'Iyd of qurban, he will have to kill two sheep, one for the vow and the other for the 'Iyd of qurban. If this person means the qurban of the 'Iyd when vowing, he kills only one sheep as the qurban. If he vows it before the days of 'Iyd, he will have to kill two, whatsoever his intention was. For, to mean something which is not fard for one to do is not to inform that one is going to do it. Also, if a person who becomes rich on one of the 'Iyd days, (let us say, on the third day), vowed to kill a sheep when he was poor on one of the 'Iyd days, (let us say, on the first day), he has to kill two sheep, for the same reason. For a rich person who has not become a hajji to vow hajj is similar to a rich person vowing a qurban on one of the days of 'Iyd of qurban. For, performing the hajj, like performing the qurban, is of two kinds: performing the hajj which is fard; and performing the supererogatory hajj. If, when vowing to go on hajj, he does not mean to become a hajji, that is, to perform the hajj which is fard, he will have to perform the hajj twice. For, if the person for whom it is wajib to perform the qurban does not mean the wajib when vowing the qurban, it will come to mean the supererogatory qurban and so the vow will be sahih. Likewise, if the hajj which is fard is not meant when vowing to go on hajj, it will come to mean a supererogatory hajj. So the vow will be sahih, and the rich person will have to go on hajj twice, one for the fard, and one for the vow. The case is not so with vowing for the fast in Ramadan or, for example, vowing noon prayer or vowing to become a hajji. Only the fard is meant when they are said. They have no supererogatory forms. Because the person vowing them means only the fard, the vow is not sahih. This means to say that something which can be both fard and supererogatory can be vowed. Its fard form shouldn't be meant when vowing. This applies to vowing namaz, fasting, hajj, and qurban. A person who vows to fast in Ramadan does not have to fulfill anything. He only fulfills his fast of Ramadan, which is fard.

It is permissible for the poor as well as for the rich to vow a qurban. Qurban means a sheep, goat, ox, or camel killed on one of the first three days of the 'Iyd, which is wajib for the rich and supererogatory for the poor. A person who has vowed ten sheep kills ten sheep within the three days of the 'Iyd. If they are not killed within that time, he gives them alive as alms if he still possesses them. For, the commandment is to kill only one sheep. That the vowed number is ten shows that he did not communicate that he would perform the qurban which is wajib. The vowed qurban must be performed on one of the three certain days. If the animals are killed before these days the qurban has not been performed and the nazr has not been performed. If the vowed qurban is not performed by the end of the three certain days, its equivalent in gold or silver or the animal itself is given alive as alms to the poor. If he kills it after the three certain days ('Iyd days) and gives the meat to the poor, the value of the meat shouldn't be less than the value of the animal was when it was alive. If it is less, he will have to give the difference in money to the poor. But if a person vows to kill a sheep instead of mentioning the name of qurban, he may kill it at any place and at any time he likes, including the days of the of 'Iyd of qurban, even if he has appointed the time and the place.

V - The thing vowed should be a piece of property, and it shouldn't be more than one's property or belong to someone else. For example, if a person who has a hundred pounds vows to give a thousand pounds as alms, he will have to give a hundred pounds. If he vows to give a certain number of gold coins, and then if he loses the gold coins, the nazr lapses.

It is permissible to vow to read the Qur'an or to visit the Kaba. It is permissible to vow to say a certain number of salawats for our Prophet (sallallahu alaihi wa sallam), [e.g. to say the prayer of Dalail-i-khayrat or Jaliyet-ul-akdar].

[It is not permissible to vow a cock by saying, "I will make a qurban of a cock or kill a cock for Allah's sake." For the cock is not an animal for qurban. A person who wants to vow a cock must say, "I will kill a cock and give it to the poor for Allah's sake," and must give the cock, alive or after killing it, to the poor. Thus, he will have vowed not the qurban but the alms]. If a person who has vowed alms has also mentioned its amount, he gives that amount. If he has not mentioned the amount he pays the kaffarat for an oath, which is to give half a sa' of wheat or its equivalent to each of ten poor people.

When one's relative or friend is back from a long journey or when one is visited by a person whom one loves and respects, it is not permissible to kill an animal out of joy or reverence to the visitor or for thanks. The animal can be vowed before or after the arrival of an expected guest, and killed as a vow, that is, for Allah's sake; in this case the meat is given to the poor; the rich are not allowed to eat it. [If one says "qurban" when vowing the animal, one has to kill it on the 'Iyd of qurban]. Also, it is permissible to kill an animal with the intention of giving a special meal to the expected visitor.

It is permissible to fulfill the absolute nazr before the appointed time. But it is not sahih to fulfill the dependent nazr before the desired condition comes into being. A person who has vowed something as alms can give something else of the same value or its equivalent. He who has vowed to fast in a certain month has to fast every day in that month, and has to make qada of the omitted days. If he has not appointed the name of the month, he fasts for one month [thirty days], which he can complete in several months. If a sick person vows that he will fast for a month for Allah's sake and then dies before recovering from his illness, nothing is required. If he recovers even one day before his death and does not fast on that day, he wills an isqat for the whole month.

Whether rich or poor, a person cannot eat from the meat of the animal killed as the fulfillment of his vow, nor can he give it to people to whom it is not permissible to give zakat. Nor can he let his parents, children, wife, [or husband, if the person is a woman], eat from the meat, even if they are poor. If he should eat or let those people eat from it, he gives the equivalent of the meat eaten as alms to the poor. Of his relatives and household, whether young or old, everyone who he is permitted to give his zakat to can eat from the meat. But the rich ones cannot. If they do, the performer of the vow will have to give the equivalent of what they have eaten to the poor.

Ibni 'Abidin 'rahmat-ullahi 'alaih' says at the end of his discourse on zakat for sheep: In zakat, 'ushr, kharaj, fitra, nazr, and in all kinds of kaffarat except manumiting slaves, it is permissible to give the equivalent of property which is not mithli even if the property itself exists. [Property of zakat can be given as an equivalent for property of zakat. Other property cannot be given. Any property can be given for other kinds of property]. It is permissible to give three fat sheep instead of four thin sheep. For things that are mithli, that is, things that can be measured by weight or volume, their equivalent of the same kind cannot be given. For example, it is not permissible to give four gold coins of high carat instead of five gold coins of lower carat or four pounds of good wheat instead of five pounds of wheat of poorer quality. It is necessary to give the same amount (five gold coins or five pounds of wheat) of the better quality too. But it is permissible to give their equivalent of some other kind. For, when goods in whose comparison there is faidh (interest, usury) are of different kinds, it is permissible to give less or fewer of the better ones and more of the poorer ones. In qurban and in emancipating slaves equivalents cannot be given. For these two require shedding blood and rescuing from slavery, not giving property. Only after the 'Iyd days are over can the equivalent of the animal for qurban be given to the poor. A person who has vowed to kill two medium sheep as the qurban cannot kill a big ram as the qurban which is equal to them in value. He has to kill two. [In lieu of sheep (vowed) the same number of goats can be killed, and equal number of cattle can be offered in place of camels vowed. They do not have to be equal in weight or value.] But he who has vowed to give two medium sheep as alms (to the poor) can give a big ram which is equal to the two sheep in value. A person who has vowed a tin of low quality dates cannot give half a tin of good dates which are equal in value. For, when they are of the same kind, if their amounts are not equal when being changed for each other the act becomes faidh. It would be permissible if he gave half a tin of good barley which is of equal value.

A vow to kill an animal must be for Allah's sake without any stipulation. It is permissible to give the meat to the poor and to present the thawab for it to a wali or to an exalted religious (dead) person. Then, one must pray for the realization of one's wish for the sake of the alms and the wali (to whose soul one has presented the thawab for the alms one has given to the poor). In other words, one must do one's vows as exemplified: "If I attain this wish of mine, I will kill a sheep for Allah's sake at Ayyub [A district in Istanbul. It is situated alongside the Golden Horn. It embodies the blessed grave of hadrat Khalid Ayyub al-Ansari 'radi-Allahu ta'ala anh', one of the Sahaba. See below.], give the meat to those poor people who are neighbors to Hadrat Khalid [ When the Messenger of Allah completed his painful trek from Mecca and finally arrived in Medina, -the onerous migration has been termed 'Hijrat' (Hegira) ever since-, all the Muslims living in Medina met the blessed Prophet at the gate of the holy city, each and every one of them begging the Messenger of Allah to honor his house and be his guest. Lest anyone should be offended, the Prophet said to them, "I shall be the guest of the person in front of whose house my camel kneels down." The camel, with the blessed Prophet on its back, walked for a while and stopped and knelt down in front of hadrat Khalid Ayyub al- Ansari's house. So the Prophet stayed in his house. Years later this fortunate Sahabi joined an Islamic expedition and went to Istanbul to conquer the city. Yet the siege ended in failure and he was one of those who attained martyrdom. His blessed grave is at Ayyub, Istanbul. There is a shrine over his grave and a splendid mosque was built by the shrine. Every day thousands of Muslims visit the shrine and the mosque.], and present the thawab to his soul." An animal vowed with a stipulation of this sort cannot be killed before the realization of the wish. The animal shouldn't be killed near the grave. Also, our religion does not permit such things as fastening pieces of cloth or string on tombs or burning candles on tombs. These things are done by Christians. Candles shouldn't be burned on graves. If candles are taken to the poor people who serve the tombs and who pray there, it will cause thawab of alms. And this thawab will be presented to the dead people there. Dead people do not need candles. A believer's grave is a garden of Paradise. It is in nurs (haloes). And a disbeliever's grave is a ditch of Hell. It is full of torment. Candles will not rescue him from this torment.

It is written at the end of the chapter about the fast in Durr-ul-mukhtar: Ignorant people vow such things as money and candles for the dead. They want to approach the great awliya and get benefits from them. These vows are haram and useless. They should be vowed for Allahu ta'ala and given to the poor Muslims (serving and worshipping) in the mausoleums." While explaining these statements, Ibni Abidin says: "It is haram to go to the grave of one of the great awliya and say, 'If you find my lost property, -cure my sick relative, solve my such and such problem-, I will give this money -or food- for your sake, I will burn a candle and leave it here for your.' For a vow is done only for Allah's sake. It is disbelief to expect something from a dead person independently from Allahu ta'ala. It drives away one's iman. [He who goes to a church, sacred spring, grave or tomb and asks for something from Hadrat Isa (Jesus), Mariam (Mary), or the awliya and prays to them becomes a disbeliever. One should ask from Allahu ta'ala so that He will give for their sake. Hadrat Abdulhakim Arwasi 'quddisa sirruh' used to say that such expressions as "The Grandfather who gives promptly" are very ugly and cause disbelief]. One should say, 'O my Allah! I vow that if You cure my sick relative I will give this money to the poor people living near that wali's tomb and present the thawab to the Wali's soul.' It is haram for the rich to accept things given in fulfillment of such vows. Property which is not given as alms to the poor is not acceptable as a vow. For example, such vows as burning candles on graves, lighting candles (or lights) on minarets, saying mawlids loudly in mosques like songs and dance music are not acceptable. It is haram and useless to pay or take money for such things." It is written at the end of 'Uqud-ud-duriyya that it is bidat to use more lights than usual in mosques on sacred nights. The same is written in the chapter about the rules for a mosque in Ashbah.

Some people make a vow by saying, "Table of Zachariah." They put 40 kinds of fruit on a table, and then they invite their neighbors and close friends to eat from this table. They expect that the wishes they make as they eat at these tables will come true. Such a vow is bidat. It is a Jewish custom. It is haram for anyone, except a poor person, to eat from something that has been vowed. To cause bidat and haram is a grave sin.

It is permissible to vow to kill an animal when laying a foundation or when one's sick relative recovers and then to give the meat as alms to the poor. It produces thawab for alms.