Undoubtedly keeping promises and keeping one’s word are attributes of a believer, and breaking promises is one of the attributes of a hypocrite. The Prophet (peace and blessings be upon him) is reported to have said: “There are four (characteristics), whoever has them is a hypocrite, and whoever has one of the four has a characteristic of hypocrisy unless he gives it up: when he speaks, he lies; when he makes a promise he breaks it; what he makes a pledge he betrays it; and when he disputes he resorts to foul language.” (Reported by al-Bukhari and Muslim)
Sheikh M. S. Al-Munajjid, a prominent Saudi Muslim lecturer and author, states the following: “The believer who makes promises to people and breaks his promise may have an excuse or he may not. If he has an excuse, then there is no sin on him, but if he does not have an excuse then he is a sinner.
As far as we know, there is no text that makes any exception regarding the prohibition of breaking promises, but it may be that promises are broken in situations where the believer is excused. For example:
1-Forgetting
Allah has forgiven us for forgetfulness whereby obligatory actions are omitted or impermissible actions are committed. Allah says, “Our Lord! Punish us not if we forget or fall into error” (Al-Baqarah: 286) And Allah has said: “Yes.” (Reported by Muslim)
According to another version, Allah said: “I will do that.” (Reported by Muslim)
Thus, whoever makes a promise to someone then forgets the promise or forgets to do it at the time stated, there is no sin on him.
2-Being forced
Being forced is one of the impediments that make it permissible for a Muslim to break his promise, such as one who is detained or is prevented from fulfilling his promise, or who is threatened with a painful punishment.
Ibn `Abbas (may allah be pleased with him) reported that the Prophet (peace and blessings be upon him) said: “Allah has forgiven my ummah for their mistakes, what they forget and what they are forced to do.”
3- Promising to do something haram or to not do something obligatory
Whoever promises someone that he will do something haram for him, or that he will not do something that is obligatory, it is not permissible for him to fulfill that promise. This may be supported by the Hadith of `A’ishah (may Allah be pleased with her), which is also known as the Hadith of Barirah (narrated by Al-Bukhari and Muslim). `A’ishah (may Allah be pleased with her) had promised Barirah’s former masters that the wala’ of Barirah [the right to inherit from her when she dies, which is the right of the one who sets a slave free] would belong to them even though `A’ishah (may Allah be pleased with her) was the one who was going to set Barirah free. But she did not keep this promise because they had gone against the Shari`ah and they knew that the right of wala’ belonged to the one who set the slave free, so how could `A’ishah set her free and then the wala’ of Barirah belong to them?
Imam Al-Shafi`i said: When news of that reached them, the one who had stipulated a condition that was contrary to the ruling of Allah and His Messenger was a sinner, and there are penalties and discipline for the sinner. One of the ways in which the sinners are disciplined is that their conditions are rendered null and void so as to deter them and others from doing likewise. This is one of the best forms of discipline.
4-Something unforeseen happening
If something unforeseen happens to the one who made the promise, such as sickness, the death of a relative, or the breakdown of his means of transportation, et cetera, there are many excuses, which all come under the heading of the verse “Allah burdens not a person beyond his scope” (Al-Baqarah: 286)