Al-Bara' bin `Azib (May Allah be pleased with them) reported

Messenger of Allah (ﷺ) 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).

[Al-Bukhari and Muslim].