Musnad Ahmad 952:2

Rab'i ibn Ibrahim—the brother of Isma'il ibn 'Ulayyah, and he praised him well, and it was said that he was preferred over Isma'il—narrated to us, saying: 'Abd al-Rahman ibn Ishaq narrated to us, from Muhammad ibn Zayd ibn al-Muhajir, from 'Umayr, the freed slave of Abi al-Lahm, who said: I witnessed Khaybar with my masters. The Messenger of Allah (peace and blessings of Allah be upon him) gave an order regarding me, so a sword was hung upon me, but I was dragging it. He said: It was said to him, "He is an owned slave." He said: "So he ordered for me something from the miscellaneous goods." He said: And I presented to him a ruqyah (incantation) with which I used to treat the insane during the Jahiliyyah. He said: "Discard such and such from it, and treat with what remains." Muhammad ibn Zayd said: "And I caught up with him while he was treating the insane with it."