Mukhtasar Muslim

It is narrated from Sayyiduna Miqdad bin Aswad (may Allah be pleased with him) that he said: "O Messenger of Allah! If I confront a disbeliever, he fights with me and cuts off one of my hands with a sword, then takes shelter behind a tree and says, 'I have submitted to Allah,' should I kill him after he has said this?" The Prophet (peace and blessings be upon him) said, "Do not kill him." I said, "O Messenger of Allah! He has cut off my hand, then said this—should I kill him?" The Prophet (peace and blessings be upon him) said, "Do not kill him." (Even though you have suffered harm and injury from him.) "If you kill him, then his state will be like yours before you killed him, and your state will be like his before he said this statement."