Truthfulness in treaties is from the virtues of morality, which a believer should possess, and Allah SWA says commending some of his slaves: (Those who faithfully observe their trusts and their promises) surah Al-Mu’minun, and Allah says: (And those who keep their promises if they make them)- surah Al-Baqarah. He also says: (Among the Believers are men who have been true to their promise with Allah: of them some have completed their vow (to the extreme), and some (still) wait: but they have never changed (their determination) in the least)- surah Al-Ahzab.

Promises can be classified into promises with Allah SWA, and promises made with people, and Dr. Abd Al Muez Hareez a teacher of jurisprudence and its principles in the University of Jordan- explains types of promises and he says:

The promise with Allah obliges a person to keep it with Allah as much as he can. If he has made a promise over something that he was unable to keep, then to detach himself from its burden, he must offer expiation for the oath, except in a case if he detaches himself from the oath he must commit a sin. This is exempted because whoever made a promise to Allah to follow his commands does not free himself from it, but whoever makes an oath with Allah to perform an act of worship that falls under recommended actions, then he saw in himself the inability to continue that act then he may free himself from the oath by paying the expiation. 

Regarding the promises made with people they are of many types: all of them come under the saying of Allah SWA: “O you who have believed keep your promises”, and His saying SWA: “And keep your promises verily the promises will be questioned”. This is applicable on the promises made with people that involves the obedience of Allah. However, if the promise is made with people on engaging in sin and disobedience, then he is not allowed to keep it, and it is forbidden to take such an oath.

In the case of breaking an oath made with people, if the act engaged is permissible or allowed, then the oath is only kept with the consent of both sides, or telling the other party according to his ability and his oath on which he is held upon. As for the oath made on disobedience then there is no need to inform or go back to the other person to break the oath, because the oath made is forbidden and is considered an invalid one.