Riyad as-Salihin 895
Abu Hurairah (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) said, "Every Muslim has five rights over another Muslim (i.e., he has to perform five duties for another Muslim): to return the greetings, to visit the sick, to accompany funeral processions, to accept an invitation, to respond to the sneezer [i.e., to say: 'Yarhamuk-Allah (may Allah bestow His Mercy on you),' when the sneezer praises Allah] ." [Al-Bukhari and Muslim] .
وعن أبي هريرة رضي الله عنه أن رسول الله صلى  الله عليه وسلم  قال‏:‏ ‏"‏حق المسلم علي المسلم خمس‏:‏ رد السلام، وعيادة المريض، واتباع الجنائز، وإجابة الدعوة، وتشميت العاطس” ‏(‏‏(‏متفق عليه‏)‏‏)‏ ‏.‏