Musannaf Ibn Abi Shayba 36:205

'Abd al-Rahim narrated to us, from Muhammad ibn Ishaq, from Muhammad ibn 'Amr, from 'Ata', who said: Suhayl ibn 'Amr was a man whose lower lip protruded. On the day he was taken prisoner at Badr, 'Umar ibn al-Khattab said to the Messenger of Allah (may Allah bless him and grant him peace), "O Messenger of Allah, let me pull out his two lower incisors so that his tongue will hang out, and he will never stand against you as an orator in any place ever again." He (the Prophet) said, "I will not mutilate, lest Allah mutilate me."