Narrated Abu Hurairah رضي الله عنه Allah's messenger 
said:
A Muslim has six duties towards another Muslim:
When you meet him, you salute him;
when he invites you, accept it;
when he asks your advice, give it to him;
when he sneezes and praises Allah, say 'May Allah have mercy on you';
when he is ill, visit him;
and when he dies, follow his funeral."
(reported by Muslim)
