Sahih al-Bukhari 6865, 6866

ʿAbdan narrated to us: ʿAbdullah narrated to us: Yunus narrated to us, from al-Zuhri. ʿAtaʾ ibn Yazid narrated to us that ʿUbaydullah ibn ʿAdi told him that al-Miqdad ibn ʿAmr al-Kindi, an ally of Banu Zuhra who had been with the Prophet (peace and blessings be upon him) at Badr, told him: I said, “Messenger of God, if I meet an unbeliever and we fight, and he strikes my hand with his sword and cuts it off, then takes refuge behind a tree and says, ‘I submit to God,’ may I kill him after he has said that?” The Messenger of God (peace and blessings be upon him) said, “Do not kill him.” I said, “Messenger of God, he cut off one of my hands, and only then said it. May I kill him?” He said, “Do not kill him. If you kill him, he will be in the position you were in before you killed him, and you will be in the position he was in before he uttered the words he said.” Habib ibn Abi ʿAmra also related, from Saʿid, from Ibn ʿAbbas, that the Prophet (peace and blessings be upon him) said to al-Miqdad: “If a believing man conceals his faith among an unbelieving people, then makes his faith known and you kill him, you would be as he was when you used to conceal your faith in Mecca.”