Musnad Ahmad 952:1

Bishr ibn al-Mufaddal narrated to us, from Muhammad ibn Zayd, [who said]: Umayr, the freed slave of Abu al-Lahm, narrated to me, saying: I witnessed Khaybar with my masters, and they spoke to the Messenger of Allah, may Allah bless him and grant him peace, [about me]. So he ordered for me, and I was girded with a sword, but I was dragging it. It was informed that I was a slave, so he ordered for me some of the miscellaneous goods.