Prophet Muhammad (sal Allahu alaihi wa sallam) said, “The signs of a hypocrite are three: when he speaks he lies, when he promises he breaks it, and when entrusted he betrays his trust.”
Therefore, one must be careful not to make promises casually or to make promises that one has no intention to keep. Allah Most High mentions in the Quran the story of the man who lied and broke his promise and the recompense of such people:
“Of them, there is one who promised Allah, ‘If He bestows of His generosity on us, we shall certainly give charity and be of the righteous.’ But when He gave to them of His generosity, they hoarded it and turned away in aversion. So He punished them by putting hypocrisy into their hearts until the day they meet Him, because they broke their promise to Allah and lied.” [9:75-77]
Imam Suyuti says that the person referred to above is Thalaba ibn Hatib, who asked the Prophet (sal Allahu alaihi wa sallam) to pray that Allah would enrich him, so that he might give everyone their just due. So the Prophet supplicated for him and he became wealthy, but then he stopped coming to the Friday prayer, withdrew from the community, and refused to pay zakat.
Some time after this, Thalaba brought the Prophet (sal Allahu alaihi wa sallam) his zakat, but the Prophet told him, “Allah forbids me to accept it from you,” at which Thalaba threw handfuls of dust upon his head. In the time of Abu Bakr’s khilafat he took his zakat to Abu Bakr (radhi Allahu anhu), but he would not accept it. Then to Umar (radhi Allahu anhu), but he would not accept it either. Then he took it to Uthman (radhi Allahu anhu), but he would not accept it, and he died in the khilafat of Uthman. [Reliance of the Traveller by Ahmad ibn Naqib al-Misri]