Musnad Ahmad 32:748

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from al-Zuhri, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not envy one another, do not cut ties with one another, and do not turn your backs on one another. Be, O servants of Allah, brothers. It is not lawful for a Muslim to forsake his brother for more than three [days]."