The Holy Prophet (s.a.w.s.) respected the treaty with the Polytheists

When the power and glory of Islam was at its zenith a verse of Surah Baraat was revealed; ordering Jehad (holy war) against the polytheists. The Almighty Allah commanded the Prophet to purify the Holy Mecca from the filth of polytheism and idol worship but it was also ordered not to break the treaty with the polytheists if they did not break it. The ayat is as follows:
"Except those of the idolaters with whom you made an agreement, they have not failed you in anything and have not backed up anyone against you, so fulfill their agreement to the end of their term; surely Allah loves those who are careful (of their duty)." 
(Surah Tauba 9:4)

Abu Rafe says: "The Quraish sent me to the Holy Prophet (s.a.w.s.). When I met him, my heart became illuminated with his countenance. I said to him, "O Prophet of Allah! I do not wish to go back to the Quraish." He said, I would not act against the terms of treaty, and retain their messenger. Abu Rafe, go back to your people now and after this if you wish, you may accept Islam and join us."

Honoring the terms of the treaty with the Quraish

Huzaifa Yamani says that there was one thing that discouraged me from participating in the Battle of Badr. Abu Husael and I were going out when we came face to face with some men from the Quraish. They asked, "Do you love Muhammad?"

"We love Madinah," we replied. 
They made us promise that after reaching Madinah we shall not accompany the Holy Prophet (s.a.w.s.) in the battle. When we met the Holy Prophet (s.a.w.s.) and told him of this promise he said, 
"Do not think of joining in the battle due to this oath of yours. We shall seek the Divine assistance!"

The above two traditions are recorded in the book, "Islam and World Peace" by Syed Qutb, Pg.264.

The Kafir father took away his son

During the treaty of Hudiabiya, Sohail Ibne Umer was representing the disbelievers in negotiating with the Holy Prophet (s.a.w.s.). When it was time for drawing up the treaty and the signatures were yet to be affixed, Jundal the son of Sohail left the pack of disbelievers and went to the Muslims. Seeing that he was attracted to the Muslims, the Quraish chained his legs but he escaped with the chains intact. He went away with the Muslims and began to behave like one. When his father saw this, he came to his son and gave him a resounding slap. Then he told the Holy Prophet (s.a.w.s.), "O Muhammad! This (treaty) is the first step of reconciliation between you and us and as per its terms you have to surrender my son to me."

The Holy Prophet (s.a.w.s.) agreed to it and surrendered Jundal to his Kafir father, but upon the condition that he would be protected and not harmed. Sohail Ibne Umar agreed to this condition. When it was time to hand over Jundal to the disbelievers, Jundal protested, "O Muslims! I have become a Muslim! How will I return amongst the polytheists?"

The Holy Prophet (s.a.w.s.) told him, 
"Go! But have patience. Allah will provide ease to you in this way only. We cannot go against the terms of the treaty."

Sohail caught his son's hand and led him away. He did not remain true to his promise and tortured his son very much.

This incident proves the importance of the fulfillment of a promise. The same incident is mentioned in the exegesis of Surah Fath in Tafseer Minhajus Sadeqeen.

I will stay here all my life

The following narration is recorded in Behaarul Anwaar:
The Holy Prophet (s.a.w.s.) promised a man that he would wait for him at an appointed place near a stone. The Holy Prophet (s.a.w.s.) waited there but the man did not turn up. Morning turned into afternoon while the Holy Prophet (s.a.w.s.) stood in the blazing sun. Some of his followers saw him and said, "Please stand in some other place."

He (s.a.w.s.) replied, 
"I cannot move away from here till that man returns."

The man arrived at last. The Holy Prophet (s.a.w.s.) said, 
"If that man had not come, I would have continued to stand till death!"

Janab-e-Ismail and the fulfillment of the vow

The Holy Quran refers to Prophet Ismail as the "Truthful in Promise," in the following verse:
"And mention Ismail in the Book, surely he was truthful in (his) promise, and he was an apostle, a prophet." 
(Surah Marium 19:54)

Hazrat Ismail (a.s.) had promised to wait for a person, who did not turn up. Three nights passed but he still kept waiting. However, according to most of the scholars and well-known tradition the period of his wait was a whole year. During this time he also had to bear untold difficulties and sometimes survived on leaves.

Violation of a promise is caused by disbelief

Amirul Momineen Ali (a.s.) has mentioned that it is disbelief that causes one to go back on his word and break a vow. He says:
"By Allah, Muawiya is not more cunning than I am but he deceives and commits evil deeds. Had I not been hateful of deceit I would have been the most cunning of all men. But (the fact is that) every deceit is a sin and every sin is disobedience (of Allah), and every crafty person will have a banner by which he will be recognised on the Day of Judgment." 
(Nahjul Balagha Sermon 200)

Allamah Majlisi says that the one who commits greater sins is also referred to as a disbeliever in traditions. Hence every type of a crafty person has been called a Kafir in this sermon. It is that disbelief which has its root in the heart and which takes the form of disobedience to Allah's commands.

A Muslim is never deceitful

Amirul Momineen Ali (a.s.) has said: 
"Surely fulfillment of pledge is the twin of truth. I do not know a better shield (against the assaults of sin) than it. One who realises the reality of return (to the next world) never betrays. We are in a period when most of the people regard betrayal as wisdom. In these days the ignorant call it excellence of cunning. What is the matter with them? Allah may destroy them. One who has been through thick and thin of life finds the excuses preventing him from orders and prohibitions of Allah, but he ignores them despite capability (to succumb to them and follows the command of Allah), while one who has no restraints of religion seizes the opportunity (and accepts the excuses for not following the commands of Allah)." 
(Nahjul Balagha Sermon 42)

Violation of promise and falsehood

Some of the Mujtahids consider violation of a promise to be a kind of falsehood. Especially when at the time of promising, one has no intention of fulfilling it. Thus all the verses and tradition denouncing and prohibiting falsehood also apply here.

If there are some conditions

According to the Fatawa (religious decrees) of the leading Mujtahids, it is wajib to honour the terms and conditions of a transaction and it is obligatory to fulfill them. For example the buyer can put a condition that if the goods are defective he can return them within two months. Or the seller may put a condition that the buyer must not spoil the goods if he wishes to return them. In such situations it is wajib to honour the terms of agreement. Similarly if the landlord has restricted the use of his premises to any one except the tenant, the tenant has to observe the terms faithfully. Both the parties to a transaction have a right to lay down their terms and conditions.

Other Mujtahids state that not only is it wajib to honour the terms and conditions of a transaction but the one who has put them may enforce his rights and insist on the condition being fulfilled. For example if an employee has laid a condition that he shall be paid his salary on the first day of every month, then not only is it necessary to pay him as agreed but theemployee has a right to demand it on that day, and he can even take it without the knowledge of his employer.

At times it may happen that the conditions agreed upon are quite irrelevant to the actual transaction and not directly related to it. Even in these cases it is necessary to fulfill the obligations.

In cases where the terms and conditions are such that the parties consider it better to observe them, these conditions do not contribute a right and it is not wajib to follow them to the letter.

Fulfillment of promise is a must

In all respects, fulfillment of a promise is so much emphasised in the Quranic Verses and the traditions, that one should be extremely cautious in honouring every type of agreement and pledge. If a person has to give a promise under compulsion and he does not wish to become a sinner, he can use words like, 'May be', 'If', or 'Insha-Allah' etc. For example he can say, "Insha-Allah (If Allah wills) I will do this."

To vow or pledge after saying Insha-Allah

It is the opinion of Allamah Hilli, and other Mujtahids agree, that every vow or pledge after uttering Insha-Allah (or its translation in any other language) makes the pledge conditional to the Divine will. Hence it is not strictly wajib to fulfill it. But if it is with regard to some promise or condition (of an agreement), that concerns a wajib act or it is for the avoidance of a haraam act, it has to be observed faithfully, even after uttering Insha-Allah.

It must however be understood that the promise which is made conditional by saying 'Insha-Allah' is not binding, only when the person intends the actual meaning of the term Insha-Allah. That is, he must really mean to subject the matter to Allah's will. If he utters Insha-Allah only for the sake of seeking divine blessings then it is binding upon him to remain firm upon his vows.

It should also be clear that it is not only permitted, to disregard a promise of abstaining from a wajib act or to perform a haraam act but it is infact haraam to fulfill it. For example if one vows to punish his wife or son if they did such and such thing, it is better to disregard such vows and forgive them instead.

The Quran says: 
"And let not those of you who possess grace and abundance swear against giving to the near of kin and the poor and those who have fled in Allah's way, and they should pardon and turn away. Do you not love that Allah should forgive you?' 
(Surah Nur 24:22)

It means that Allah forgives the sins of those who forgive the wrongdoings of others.

Prophet Ayyub (a.s.) and his oath of beating his wife a hundred strokes

In a situation where, one has taken an oath in utmost seriousness to inflict punishment, and one does not wish to go against it, it is better to carry out the oath in a manner that a token punishment is given and the oath is also not violated. For example, Prophet Ayyub (a.s.) saw his wife doing something against his will. He took a vow to hit her a hundred strokes after he recovered from the illness. When he recovered, Allah ordered him, 
"And take in your hand a green branch (with a hundred twigs) and beat her (your wife) with it (once) and do not break your oath." 
(Surah Saad 38:44