Hadithcore
Al-Adab Al-Mufrad, 414
da’if· Al-Albani

Abu Hurayra reported that he heard the Prophet, (ﷺ), say, "It is not lawful for a Muslim man to refuse to speak to a believer for more than three days. When three days have passed, he should meet him and greet him. If he returns the greeting, they share in the reward. If he does not return the greeting, the one who gives the greeting is innocent of having severed relations."

حَدَّثَنَا إِسْمَاعِيلُ بْنُ أَبِي أُوَيْسٍ قَالَ‏:‏ حَدَّثَنِي مُحَمَّدُ بْنُ هِلاَلِ بْنِ أَبِي هِلاَلٍ مَوْلَى ابْنِ كَعْبٍ الْمَذْحِجِيِّ، عَنْ أَبِيهِ، أَنَّهُ سَمِعَ أَبَا هُرَيْرَةَ قَالَ‏:‏ سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ‏:‏ لاَ يَحِلُّ لِرَجُلٍ أَنْ يَهْجُرَ مُؤْمِنًا فَوْقَ ثَلاَثَةِ أَيَّامٍ، فَإِذَا مَرَّتْ ثَلاَثَةُ أَيَّامٍ فَلْيَلْقَهُ فَلْيُسَلِّمْ عَلَيْهِ، فَإِنْ رَدَّ عَلَيْهِ السَّلاَمَ فَقَدِ اشْتَرَكَا فِي الأَجْرِ، وَإِنْ لَمْ يَرُدَّ عَلَيْهِ فَقَدْ بَرِئ الْمُسْلِمُ مِنَ الْهِجْرَةِ‏.‏

References2 variants
In-Book Reference
Book 22, Hadith 18
English Reference
Book 22, Hadith 414