Sayyiduna al-Miqdad bin Amr al-Kindi (may Allah be pleased with him), the ally of Banu Zuhrah, said: "O Messenger of Allah, what do you think: if I meet a man from the disbelievers and he fights me, and cuts off one of my hands, then he takes refuge from me behind a tree and says: 'I have submitted to Allah (become Muslim)' - should I kill him, O Messenger of Allah?" The Messenger of Allah (peace and blessings be upon him) said: "Do not kill him." He said: "O Messenger of Allah, he cut off one of my hands, and then said that after cutting it off?" The Messenger of Allah (peace and blessings be upon him) said: "If you kill him, you will be in the position he was in before he said the word that he said, and he will be in the position you were in before you killed him."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17726