(9) باب السَّلاَمِ لِلْمَعْرِفَةِ وَغَيْرِ الْمَعْرِفَةِ
Narrated Abu Aiyub:
The Prophet (ﷺ) said, "It is not lawful for a Muslim to desert (not to speak to) his brother Muslim for more than three days while meeting, one turns his face to one side and the other turns his face to the other side. Lo! The better of the two is the one who starts greeting the other."
Reference: Sahih al-Bukhari 6237
In-book reference: Book 79, Hadith 11
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 8, Book 74, Hadith 254