Anas ibn Malik reports that hardly did the Holy Messenger (peace and blessings of Allah be to him) addressed us without saying: “There is no Iman in him who cannot hold a trust and no religion for him who does not keep his promise.”
(Baihaqi)
The Holy Messenger of Allah, Muhammad (peace and blessings of Allah be to him) used to inculcate the very spirit of Islam in his Companions in a very effective manner. This hadīth records one such Prophetic teaching. It brings into light two salient features of Islamic faith – holding a trust and keeping a promise. A person who willingly and knowingly fails to hold a trust or keep a promise is a grave sinner rather a hypocrite in the eyes of Allah.
When a person is entrusted with some money, secret or power, he is expected to hold it fast. And, if he fails to do so, it is not that he is merely shattering someone’s expectations; if fact, it is his lack of faith (Iman), at least to some degree, that manifests itself in his mis(deed). Similarly, when a person fails to keep a promise, it is a matter of his or her Iman.
What really lurks behind a breach of trust or promise is to cheat one’s fellow beings. In doing so, one fails to keep in view the requirements of piety and sense of accountability. That is why the Blessed Messenger used to warn his Companions and by extension all his followers against the consequences of not holding these traits