عن البراء بن عازب رضي الله عنهما
قال: أمرنا رسول الله صلى الله عليه وسلم بعيادة المريض، واتباع الجنازة، وتشميت العاطس، وإبرار المقسم، ونصر المظلوم، وإجابة الداعى، وإفشاء السلام»
Messenger of Allah (sallallahu alayhi wa sallam) has ordered us to visit the sick, to follow the funeral (of a dead believer), respond to the sneezer (i.e., by saying to him: Yarhamuk-Allah after he says: Al-hamdu lillah), to help those who vow to fulfill it, to help the oppressed, to accept the invitation extended by the inviter; and to promote greetings (i.e., saying As-Salamu Alaikum).
Riyad as-Salihin 894, Book 7, The Book of Visiting the Sick, Hadith 1. 1 min read