Sahih Bukhari
Good Manners and Form (Al-Adab)
Volume: 008 / Book Number: 073 / Hadith Number: 117
Narrated Abu Huraira:
Allah's Apostle said, "The signs of a hypocrite are three: Whenever he speaks, he tells a lie; and whenever he promises, he breaks his promise; and whenever he is entrusted, he betrays (proves to be dishonest)".