Yahya related to me from Malik from Ibn Shihab from Anas ibnMalik that the Messenger of Allah, may Allah bless him and grant himpeace, said, "Do not be angry with each other and do not envy eachother and do not turn away from each other, and be slaves of Allah,brothers. It is not halal for a muslim to shun his brother for morethan three nights."
USC-MSA web (English) reference: Book 47, Hadith 14
Arabic reference: Book 47, Hadith 1649