Fulfill the promise, surely (every) promise shall be questioned about

Also, 
"O you who believe! Fulfill the obligations." 
(Surah Maidah 5:1)

Similarly in Surah Baqarah the ayat says, 
"...and the performers of their promise when they make a promise..." 
(Surah Baqarah 2:177)

We also find the following verse: 
"O you who believe! Why do you say that which you do not do?

It is most hateful to Allah that you should say that which you do not do." 
(Surah Saff 61:2-3)

Imam Ja'far as-Sadiq (a.s.) has explained this ayat in the following manner: 
"A believer's promise to his believing brother is a vow that has no expiation (It cannot be broken). But one who goes back on his word declares his opposition and enmity to Allah, and invokes the anger of Allah." 
(Wasaelush Shia)

After this the Imam (a.s.) recited the above-mentioned ayat.

Amirul Momineen Ali (a.s.) advises Malik al-Ashtar regarding the honouring of promises: 
"Breaking a promise causes the anger of Allah." 
(Nahjul Balagha)

Ali (a.s.) also quotes the same verse after this. 
Hazrat Imam Muhammad al-Baqir (a.s.) said: 
"There are four types of sinners who are punished very soon:
a) The person who violates the pact that he has made with you, even though you have respected it. 
b) One who inflicts harm upon you even though you caused him no harm. 
c) One who has promised you something and you are faithful upon your agreement but he is unfaithful. 
d) One who wants to severe relations even though the relative wishes to continue the relationship."
(Khisaal)

Abu Malik inquired from Imam Zainul Abedin (a.s.), "Inform me about all the rules of religion." Imam (a.s.) told him, 
"To speak the truth, to judge with justice and to fulfill the promise." 
(Khisaal)

Although a vast number of traditions and ayats denounce the breaking of promises. We shall quote some selected ones.

Types of Promises

There are three types of promises:
1. Promise of Allah to His creatures. 
2. Promise of the creatures to Allah. 
3. Promises of the people among themselves.

The promise of Allah to His creatures is that of the Aalam-e-Zar (in the spiritual plane). We come to know of this promise through the Quranic ayats as well as the traditions. According to this, Allah first created the souls of all human beings and made the following covenant: That they remain upon the right path, do not associate anyone or anything with Allah, obey the commands of their Prophet, and do not follow Shaitan, Allah shall recompense them by helping them, by keeping them forever in His mercy, and give them a place in Paradise but if they do not respect their covenant, Allah will also disregard His side of the promise. It is for this very fact, that Allah says.

"...and be faithful to (your) covenant with Me, I will fulfill (My) covenant with you." 
(Surah Baqarah 2:40)

Allah also says, 
"Did I not charge you, O children of Adam, that you should not serve the Shaitan?" 
(Surah Yaseen 36:60)

The covenant that Allah took from the people in the spiritual plane also includes the oath with regard to the Wilayat (Mastership) of Amirul Momineen Ali (a.s.) and the Imams (a.s.). Numerous traditions mention this fact. It is even recorded in the various heavenly scriptures, and all the Prophets have conveyed the message of the Wilayat of the Fourteen Masoomeen (a.s.).

However, some scholars have rejected this concept of the Aalam-e-Arwah or Aalam-e-Zar. They give a different explanation to the traditions and ayats that deal with this subject. According to them Aalam-e-Arwah (the spiritual plane) is essentially the innate human nature, which is so designed by Allah (a.j.) that it is desirous of obeying Allah's command and does not desire to follow Shaitan. Of course the reasoning capacity of man directs him to follow his nature and accordingly obey Allahs orders. Hence if a man goes against Allah's command he goes against his own nature. These thinkers consider the covenant, to be the same as the innate nature given to us by Allah (a.j.). This book is not concerned with the detail of these two theories.

Anyway whether a man breaks the promise given in Aalam-e-Zar, or goes against his innate nature, he commits a greater sin. This fact has been emphasised in most ayats and traditions, and it is confirmed that honoring the covenant is wajib and not respecting it is haraam. It is also confirmed that the breaking of this first covenant can bring severe chastisement. The people are also warned of dire consequences in case of default. The traditions also inform us that serious retribution incured just for violating the first covenant, which is the greatest of the sins. Hence it is incumbent upon the people to fulfill their covenant so that Allah may also fulfill His promise.

Allah has promised to answer every prayer

One of the promises of Allah to His creatures is that He will answer every prayer, but this is only on condition that the supplicant honors this covenant with Allah (a.j.).

Jamil narrates from Imam Ja'far as-Sadiq (a.s.) who said, 
"When a man prays to Allah with a pure intention and a sincere heart, Allah answers (his prayer) after man has fulfilled his promise to Allah (a.j.). But if man prays to Allah without a pure intention and sincerity, Allah does not answer it. Has not Allah said, '...and be faithful to (your) covenant with Me, I will fulfill (My) covenant with you,' so the promise is kept only with one who keeps his own word.'
(Safinatul Behaar)

Verbal expression of a promise

The second type of promise is one that the man himself gives to Allah, like a vow or an oath. For an oath to be binding, it is necessary that it be expressed verbally. For example, if someone wants to vow to Allah and state it in Arabic language he should say 'Aahadto Allah' (I have vowed to Allah) or 'Alayya Ahadollah' (The vow for Allah is upon me). The statement of promise, oath or the vow can be in any language but expressed verbally. A vow for example may consist of saying, "if I return safe and sound from the journey, I shall give such and such amount as charity in the way of Allah."

If an oath is intended mentally and not expressed verbally, it is not binding.

Vow or oath for a useless thing

It must be remembered that a vow, oath or a promise should not be taken for a useless object. That is, the object must not be undesirable from the Islamic point of view. An oath taken to carry out some makrooh or haraam action, a vow to abstain from a wajib or a mustahab act is invalid. An oath taken for an action which is wajib and its avoidence haraam in a prevailing set of conditions, automatically becomes invalid if the conditions change. For example, a man vows to give a thousand rupees in charity if he gets well, but after he is well be becomes so poor that it is hardly possible for him to maintain his family. In these circumstances the vow is considered invalid and it is not wajib on him to fulfill it.

Vow should be for a useful aim

In conclusion it can be said that an oath should be taken if it is acceptable from the Shariat point of view. In any case an oath should be taken when common sense dictates that the oath serves some useful purpose, either by carrying out an action or by abstaining from it. For example to walk and exercise etc. which are beneficient and Mubah (permitted) actions, and to abstain from smoking which is harmful to health although Mubah.

Conditional and absolute covenant

Just as in the case of oath and vow, a covenant is also either conditional or absolute. An example of an absolute covenant is when a man says, "I make covenant with Allah that I shall perform such and such good action." Then this shall become binding upon him. If he does not do so he would have committed a Greater sin. In addition he also has to pay the penalty. The conditional covenant is the one when the person attaches some conditions. For example, he may say, "If Allah gives me a son, I will perform such and such good deed." Then that good deed becomes wajib upon him only when he gets a son. Once the condition is fulfilled it will also be haraam for him to leave the deed undone and he will have to pay the additional penalty also.

Three types of covenant with Allah

Actually a vow and an oath is also a covenant with Almighty Allah. Therefore a covenant is of three types. One is the covenant itself and of the other two one is a vow and the other an oath. It is only due to Divine Mercy that man is given a choice of three kinds of covenants in case he wishes to avoid the risk of being liable for keeping sixty fasts etc. Hence, he can make a vow or take an Islamic oath.

Expiation of a vow or a covenant

Breaking of a covenant, whether absolute or conditional, is haraam. The expiation becomes wajib in case of default. It is the same penalty as that of breaking or omitting, without any reason, a fast of the month of Ramazan, i.e. feeding sixty poor people, keeping sixty fasts or freeing a slave.

If a vow is broken its kaffarah (expiation) is same as that of breaking an oath. That is, feeding, or clothing ten poor people or freeing a slave; but if he cannot do any of these then it is wajib for him to keep three fasts.

Breaking of promise and hypocrisy

Breaking of a promise is a very serious sin. It is a sin that sows the seed of hypocrisy in the heart of the person who commits it. The person dies in a state of disbelief and is raised with the hypocrites on the Day of Judgment. The Holy Quran says: 
"And there are those of them who made a covenant with Allah: If He gives us out of His grace we will certainly give alms and we will certainly be of the good. But when He gave them out of His grace, they become niggardly of it and they turned back and they withdrew. So He made hypocrisy to follow as a consequence into their hearts till the day when they shall meet Him because they failed to perform towards Allah what they had promised Him and because they told lies." 
(Surah Tauba 9:75-77)

The Shaan-e-Nuzool (circumstances of Revelation) of this ayat, according to Tafseer Minhaj us-sadeqeen is as follows: "Thulbe Ibne Khatib was a very staunch and a prominent Christian. One day he came to the Holy Prophet (s.a.w.s.). He began to complain of his poverty, and requested the Holy Prophet (s.a.w.s.) to pray for him. The Holy prophet (s.a.w.s.) advised him, "Do not emphasise upon this prayer of yours but be patient in your circumstances. Too much of wealth is dangerous for you. If you are grateful for this favour it is better than too much of wealth that makes you unthankful. By Allah if I pray that mountains become gold and silver and move with me, Allah shall cause it to be so but I know that an honourable hereafter is better, and those who are well provided in this world have a difficult hereafter. So, follow the Prophet of Allah (a.j.) and accept his advice."

But Thulbe the Christian did not follow the advice of the Holy Prophet (s.a.w.s.) and again he came back to him with his entreaty and said: "O Prophet of Allah! I make a covenant to Allah that if He gives me abundant wealth I shall spend it upon the deserving ones and do good through it."

When he persisted in his request, the Holy Prophet (s.a.w.s.) prayed for the removal of his property.

Allah gave abundant increase in his livestock; and he became a Muslim. His animals multiplied and he became so busy in supervising them that he stopped praying behind the Holy Prophet (s.a.w.s.) in the congregational prayers. He prayed only the morning and the evening prayers. Then his herd became so bulky that the surrounding area of Madinah was not sufficient any more. He took his animals to the outskirts of the town and settled there. Now he was deprived of praying the daily prayers behind the Holy Prophet (s.a.w.s.). Still he continued to come to Madinah for the Friday prayers. Then his business expanded beyond the valleys surrounding Madinah. Finally he could not even attend the Friday prayers.

One day the Holy Prophet (s.a.w.s.) asked his companions, "Why is Thulbe not attending the congregation?" The people replied, "He has so many goats and sheep that a single valley is unable to accommodate them. Now he has moved to such and such valley and settled there. The Holy Prophet (s.a.w.s.) upon hearing this said, 
"Woe be upon Thulbe, Woe be upon Thulbe, Woe be upon Thulbe!"

Later when it was wajib to pay zakat due to the revelation of the verse of Zakat, the Holy Prophet (s.a.w.s.) summoned one of his followers and gave him this verse in writing and sent with him a tribesman of Bani Salim. The Prophet ordered, "After you have collected Zakat from Thulbe go to such and such good man and collect it from him too." Both of them went to Thulbe. They showed him the Quranic verse and also gave him the letter of the Holy Prophet (s.a.w.s.) containing the rules of Zakat. Thulbe had become so much attached to his wealth that he said, "Muhammad is collecting Jiziya from us! Go somewhere else! Meanwhile I shall think upon it."

The two men went to this righteous person (of the tribe of Bani Salim). When he saw the ayat and the letter of the Holy Prophet (s.a.w.s.), he said, "I hear and I obey the command of Allah and the Prophet (s.a.w.s.)."

He went among his camels and selected the best ones for Zakat and said, "Please take these for the Messenger of Allah (s.a.w.s.)." The agents told him that it was not wajib to give the best of the camels. He said, "How can I not offer the best for Allah and His Prophet (s.a.w.s.)?"

Then these two men came back to Thulbe. The wretched fellow repeated his previous objection and refused to pay Zakat.

When the Holy Prophet (s.a.w.s.) heard of this incident he said just once, "Woe be upon Thulbe!" Then the Holy Prophet (s.a.w.s.) prayed for the well being of the one who had paid the Zakat willingly.

The companions used to wonder why Thulbe had not accepted the advice of the Holy Prophet (s.a.w.s.) and saved himself from apostasy! (Zakat is one of the Dhururiyaat-e-Deen and one who says that Zakat is not wajib has apositisised and is no more a Muslim!) The ayats quoted before this discussion were revealed for Thulbe.

Mutual covenants and agreements

The third type of promise is when people form actual covenants and agreements. The ayats and the traditions state that it is wajib to fulfill this type of promise and it is haraam to go against them.

For example in Surah Bani Israel: 
"...and fulfill the promise; Surely (every) promise shall be questioned about." 
(Surah Bani Israel 17:34)

Similarly the Quran describes truthful and the pious people thus,
"...and those who fulfill their promise when they make a promise.." 
(Surah Baqarah 2:177)

Also when describing those who shall be saved from Hell and earn Paradise, Allah says, 
"And those who are keepers of their trusts and their covenant." 
(Surah Momin 23:8)

Imam Ja'far as-Sadiq (a.s.) says, 
"To keep your word to your believing brother is wajib like a vow, even though there is no expiation for going against it."

The Holy Prophet (s.a.w.s.) said: 
"One who has belief in Allah and in last day (Qiyamat) must keep his word when he promises." 
(Usool-e-Kafi)

Thus keeping a promise is a fulfillment for the belief in Allah and the Day of Qiyamat. Similarly, the beginning verses of Surah Saff have also denounced the breaking of promise and clearly prove that non-fulfillment of a promise (of every type) is haraam.