Musnad Abu Ya'la al-Mawsili 118:77

Wahb ibn Baqiyyah al-Wasiti narrated to us, Khalid informed us, from Abd al-Rahman ibn Ishaq, from al-Zuhri, from Anas ibn Malik, from the Prophet (may Allah bless him and grant him peace), who said: "Do not envy one another, do not outbid one another, do not hate one another, and do not turn your backs on one another. Be, O servants of Allah, brothers. It is not lawful for a man to forsake his brother for more than three days."