There goes a famous story about an event in the life of Ali, who was one of the closest companions of Muhammad (the Prophet of Islam).
Ali ibn Abi Talib was once fighting in battle, when a certain champion from the opponent’s army attacked him. During the fight, Ali got the (upper) hand against him. He quickly raised his sword and was hurrying to kill him, when the man spat in Ali’s face. At that moment, Ali stepped aside, leaving the man alone. The man asked, “You could have killed me, why did you stop? Ali replied saying, “I have no personal animosity toward you. I was fighting you because of your disbelief in and rebellion against God. If I had killed you after you spat in my face, it would have been because of my personal anger and desire for revenge, which I do not wish to take.”
In another famous narration, Muhammad once asked his Companions, “Whom among you do you consider a strong man?” They replied, “The one who can defeat so-and-so in a wrestling contest.” He said, “That is not so; a strong man is the one who can control himself when he is angry”.