Musnad Abu Ya'la al-Mawsili 13:1

'Abd al-Rahman ibn Salih narrated to us, Yunus ibn Bukayr narrated to us, from Muhammad ibn Ishaq, who said: Dawud ibn al-Husayn narrated to me, from 'Abd al-Rahman ibn 'Uqbah, from his father, 'Uqbah, the freed slave of Jabir ibn 'Atik al-Ansari, who said: I witnessed Uhud with my master, and I struck a man from the polytheists. When I killed him, I said, "Take it from me, and I am the Persian man." This reached the Messenger of Allah, may Allah bless him and grant him peace, and he said: "Why did he not say, 'Take it, and I am the Ansari man'? For the freed slave of a people is one of them."