Abu Huraira reported Allaah's Messenger (sallAllaahu alayhi wa sallam) as saying: Six are the rights of a Muslim over another Muslim. It was said to him: Allaah's Messenger, what are these? Thereupon he said:

1 - When you meet him, offer him greetings
2 - when he invites you to a feast accept it
3 - when he seeks your council give him
4 - when he sneezes and says:" All praise is due to Allaah," you say Yarhamuk Allaah (may Allaah show mercy to you) ;
5 - when he fails ill visit him
6 - and when he dies follow his funeral.

Sahih Muslim