The Messenger of Allah ﷺ said, "It is not lawful for a Muslim to shun his brother for more than three days, where they meet and one turns away and the other turns away. The better of the two is the one who begins with the greeting of peace."
حدثنا ابن أبي عمر حدثنا سفيان حدثنا الزهري ح قال وحدثنا سعيد بن عبد الرحمن حدثنا سفيان عن الزهري عن عطاء بن يزيد الليثي
أن رسول الله ﷺ قال لا يحل لمسلم أن يهجر أخاه فوق ثلاث يلتقيان فيصد هذا ويصد هذا وخيرهما الذي يبدأ بالسلام
Its graded as agreed upon [by Bukhari and Muslim]. Bukhari reported it in the Book of Seeking Permission, Chapter on Greeting Those You Know and Those You Do Not Know, hadith no. 6237, and Muslim, hadith no. 2560, from the hadith of Sufyan bin Uyayna with this wording.There are other reports on this subject from Abdullah bin Masud [Bazzar in Kashf Astar, 2/437, hadith no. 2050, and Hakim graded it sahih, 1/22, and Dhahabi agreed with him], Anas [to come, 1935], Abu Hurairah [Abu Dawud, hadith no. 4912], Hisham bin Amir [Ahmad, 4/20, and Bukhari in Adab al-Mufrad, hadith nos. 402, 407], and Abu Hind Dari [I did not find it].