Musnad Ahmad 30:1988

Abu Nu'aym narrated to us, he said: Sufyan narrated to us, from Salih ibn Nabhan, from Abu Hurayrah, he said: The Messenger of Allah, may Allah bless him and grant him peace, said: "Do not hate one another, and do not turn your backs on one another, and do not outbid one another (to deceive), and be, O servants of Allah, brothers."