Sahih al-Bukhari 6077
Narrated Abu Aiyub Al-Ansari:
Allah's Messenger (ﷺ) said, "It is not lawful for a man to desert his brother Muslim for more than three 
nights. (It is unlawful for them that) when they meet, one of them turns his face away from the other, 
and the other turns his face from the former, and the better of the two will be the one who greets the 
other first."
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنِ ابْنِ شِهَابٍ، عَنْ عَطَاءِ بْنِ يَزِيدَ اللَّيْثِيِّ، عَنْ أَبِي أَيُّوبَ الأَنْصَارِيِّ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏
"‏ لاَ يَحِلُّ لِرَجُلٍ أَنْ يَهْجُرَ أَخَاهُ فَوْقَ ثَلاَثِ لَيَالٍ، يَلْتَقِيَانِ فَيُعْرِضُ هَذَا وَيُعْرِضُ هَذَا، وَخَيْرُهُمَا الَّذِي يَبْدَأُ بِالسَّلاَمِ ‏"‏‏.‏