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: 6313
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: The strong-man is not one who wrestles well but the strong man is one who controls himself when he is in a fit of rage.