From Sahih Bukhari (Hadith 1240):
Narrated Abu Huraira:I heard Allah's Messenger (ﷺ) saying, "The rights of a Muslim on the Muslims are five: to respond to the salaam, visiting the sick, to follow the funeral processions, to accept an invitation, and to reply to those who sneeze. (see Hadith)
Reference: Bukhari 1240