Narrated AbuHurayrah:

The Prophet ﷺ said: It is not allowable for a believer to keep from a believer for more than three days. If three days pass, he should meet him and give him a salutation, and if he replies to it they will both have shared in the reward; but if he does not reply he will bear his sin (according to Ahmad's version) and the one who gives the salutation will have come forth from the sin of keeping apart.

حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ عُمَرَ بْنِ مَيْسَرَةَ، وَأَحْمَدُ بْنُ سَعِيدٍ السَّرْخَسِيُّ، أَنَّ أَبَا عَامِرٍ، أَخْبَرَهُمْ قَالَ حَدَّثَنَا مُحَمَّدُ بْنُ هِلاَلٍ، قَالَ حَدَّثَنِي أَبِي، عَنْ أَبِي هُرَيْرَةَ، أَنَّ النَّبِيَّ ﷺ قَالَ " لاَ يَحِلُّ لِمُؤْمِنٍ أَنْ يَهْجُرَ مُؤْمِنًا فَوْقَ ثَلاَثٍ فَإِنْ مَرَّتْ بِهِ ثَلاَثٌ فَلْيَلْقَهُ فَلْيُسَلِّمْ عَلَيْهِ فَإِنْ رَدَّ عَلَيْهِ السَّلاَمَ فَقَدِ اشْتَرَكَا فِي الأَجْرِ وَإِنْ لَمْ يَرُدَّ عَلَيْهِ فَقَدْ بَاءَ بِالإِثْمِ " . زَادَ أَحْمَدُ " وَخَرَجَ الْمُسَلِّمُ مِنَ الْهِجْرَةِ " .