The reciter: 'Abdan narrated to us, 'Abdullah narrated to us, Yunus narrated to us from al-Zuhri, 'Ata ibn Yazid narrated to us that 'Ubayd Allah ibn 'Ubayd narrated to him: that al-Miqdad ibn 'Amr al-Khanda'i, the ally of Banu Zuhrah, narrated to him, and he had witnessed Badr with the Prophet (peace and blessings be upon him), that he said:
O Allah's Apostle! If I meet an unbeliever and we have a fight, and he strikes my hand with the sword and cuts it off, and then takes refuge from me under a tree, and says, 'I have surrendered to Allah (i.e. embraced Islam),' may I kill him after he has said so?" Allah's Messenger (ﷺ) said, "Do not kill him." Al- Miqdad said, "But O Allah's Messenger (ﷺ)! He had chopped off one of my hands and he said that after he had cut it off. May I kill him?" The Prophet (ﷺ) said. "Do not kill him for if you kill him, he would be in the position in which you had been before you kill him, and you would be in the position in which he was before he said the sentence."
يا رسول الله، إني لقيت كافرا فاقتتلنا، فضرب يدي بالسيف فقطعها، ثم لاذ بشجرة، وقال: أسلمت لله، آقتله بعد أن قالها؟ قال رسول الله صلى الله عليه وسلم: لا تقتله قال: يا رسول الله، فإنه طرح إحدى يدي، ثم قال ذلك بعد ما قطعها، آقتله؟ قال: لا تقتله، فإن قتلته فإنه بمنزلتك قبل أن تقتله، وأنت بمنزلته قبل أن يقول كلمته التي قال Sahih al-Bukhari 6865, 6866