Sahih Muslim
The Book of Virtue, Good Manners and Joining of the Ties of Relationship (Kitab Al-Birr was-Salat-I-wal-Adab)
Book Number: 032 / Hadith Number: 6301
Abu Huraira reported that he heard Allah's Messenger (may peace be upon him) as saying: The worst amongst people is one with the double face. He comes to some people with one face and to others with the other face.