Undoubtedly keeping promises and keeping one’s word are attributes of the believers, and breaking promises is one of the attributes of the hypocrites but it is not kufr. It is narrated from `Abdullah ibn `Amr (may Allah be pleased with him) that Prophet Muhammad (peace and blessings be upon him) 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; when he makes a pledge, he betrays it; and when he disputes, he resorts to foul language” (Al-Bukhari and Muslim).
Additionally, Almighty Allah said in the sacred verse: [Those who break the covenant of Allah after ratifying it and sever that which Allah ordered to be joined and (who) make mischief in the earth: Those are they who are the losers] (Al-Baqarah 2:27). In explanation of this verse, Imam Al-Qurtubi said, “This verse is proof that making a promise on oneself and abiding by it is permissible and it is impermissible to break it.”
In regard to this issue, Zeinab Al-`Alawani, an instructor in fiqh and Islamic studies at the Graduate School of Islamic and Social Sciences inAshburn, Virginia, the US, said: It is not an issue of kufr or shirk. Breaking a promise, albeit being a common practice nowadays, is one of the characteristics or signs of hypocrisy. Prophet Muhammad (peace and blessings be upon him) said, “Three are the signs of hypocrisy: If he speaks, he tells lies; if he promises, he breaks his promise; and if he is entrusted with something, he proves to be dishonest.”
Therefore, a Muslim should try to avoid or give up this evil and shameful practice. It is not to be underestimated at all, and it is not to be overestimated either. One of the qualities of Muslims as stated in the Qur’an is that they honor their commitments.