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: 6302
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: You will find the worst amongst the people one having double face. He comes to some people with one face and to the others with the other face.