(3) باب مِنْ حَقِّ الْمُسْلِمِ لِلْمُسْلِمِ رَدُّ السَّلاَمِ
Abu Huraira reported Allah's Messenger (ﷺ) as saying:
Six are the rights of a Muslim over another Muslim. It was said to him: Allah's Messenger, what are these? Thereupon he said: When you meet him, offer him greetings;when he invites you to a feast accept it. when he seeks your council give him, and when he sneezes and says:" All praise is due to Allah," you say Yarhamuk Allah (may Allah show mercy to you) ; and when he fails ill visit him; and when he dies follow his bier.
Reference: Sahih Muslim 2162 b
In-book reference: Book 39, Hadith 6
USC-MSA web (English) reference(deprecated numbering scheme): Book 26, Hadith 5379