Musnad Ahmad 662:0

Narrated to us by Harmalah al-Anbari, who said: Narrated to us by Ibn Wahb, who said: Informed me Yunus, from Ibn Shihab, from Anas ibn Malik, that the Messenger of Allah (ﷺ) said: "Do not hate one another, do not envy one another, and do not turn away from one another. Be, O servants of Allah, brothers. It is not lawful for a Muslim to shun his brother for more than three nights."