Musannaf Ibn Abi Shayba 36:450

Narrated to us Sharik, from Abu Ishaq, from al-Bara’, who said: No, by Allah, the Messenger of Allah (may Allah bless him and grant him peace) did not turn his back on the day of Hunayn. He said: And al-Abbas and Abu Sufyan were holding the bridle of his mule, while he was saying: "I am the Prophet, there is no lie; I am the son of Abd al-Muttalib."