Narrated Abu Huraira:
The Prophet (peace be upon him) said, “The signs of a hypocrite are three:
Whenever he speaks, he tells a lie.
Whenever he promises, he always breaks it (his promise ).
If you trust him, he proves to be dishonest. (If you keep something as a trust with him, he will not return it.)”
Sahih al-Bukhari, Vol. 1, Book 2, Hadith 26