From Sahih Bukhari (Hadith 6076):
Narrated Anas bin Malik:Allah's Messenger (ﷺ) 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
Reference: Bukhari 6076