Musnad Ahmad 658:26

Mu'awiyah ibn Hisham narrated to us, Sufyan narrated to us, from Abu Ishaq, from al-Bara', who said: "Not all of the hadith did we hear from the Messenger of Allah, may Allah bless him and grant him peace; our companions used to narrate to us from him. The tending of camels used to keep us occupied away from him."