Musnad Ahmad 490:2

Sufyan ibn 'Uyaynah narrated to us, 'Abd al-Malik ibn Abjar narrated to me, from Iyad ibn Laqit, from Abu Rimthah, who said: I came to the Messenger of Allah (peace and blessings of Allah be upon him) with my father. He saw the [seal of prophethood] on his back and said: "O Messenger of Allah, shall I treat it for you, for I am a physician?" He said: "You are a companion, and Allah is the Physician." He said: "Who is this with you?" He said: "My son; I bear witness to him." He said: "As for him, he does not commit a crime against you, and you do not commit a crime against him." 'Abdullah said: My father said: "The name of Abu Rimthah is Rifa'ah ibn Yathribi."