Narrated by Anas bin Malik (Radiyallaahu ‘anhu):

Allah’s Apostle (Sallallaahu Alayhi Wasallam) said,

"Do not hate one another, nor be jealous of one another; and do not desert one another, but O Allah’s worshipers! Be Brothers! And it is unlawful for a Muslim to desert his brother Muslim (and not to talk to him) for more than three nights."

Sahih Al-Bukhari Volume: 8 ; Number: 99