Muwatta Malik, Book 47, Hadith 13 (USC-MSA) ⓘ

Yahya related to me from Malik from Ibn Shihab from Ata ibn Yazid al-Laythi from Abu Ayyub al-Ansari that the Messenger of Allah, may Allah bless him and grant him peace, said, "It is not halal for a muslim to shun his brother for more than three nights, that is they meet, and this one turns away and that one turns away. The better of the two is the one who says the greeting first."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ عَطَاءِ بْنِ يَزِيدَ اللَّيْثِيِّ، عَنْ أَبِي أَيُّوبَ الأَنْصَارِيِّ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ لاَ يَحِلُّ لِمُسْلِمٍ أَنْ يُهَاجِرَ أَخَاهُ فَوْقَ ثَلاَثِ لَيَالٍ يَلْتَقِيَانِ فَيُعْرِضُ هَذَا وَيُعْرِضُ هَذَا وَخَيْرُهُمَا الَّذِي يَبْدَأُ بِالسَّلاَمِ ‏" ‏ ‏.‏