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: 6326
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: When any one of you fights with his brother, he should avoid the face.