There are six rights of a Muslim upon a Muslim

*Sayyiduna Abu Hurairah (RadhiAllaho anho) narrates
that Rasulullah (Sallallahu Alaihi Wasallam) said:
"A believer owes another believer five rights:
responding to greetings,
visiting him in illness,
following his funeral,
accepting his invitation,
and saying `Yarhamuk-Allah (May Allah have mercy on you),'
when he says `Al-hamdu lillah (Praise be to Allah)'
after sneezing".
[Al-Bukhari and Muslim].*

Muslim's narration is,
"There are six rights of a Muslim upon a Muslim:
When you meet him, greet him;
when he invites you, respond to him;
when he seeks counsel, give him advice;
when he sneezes and praises Allah,
say to him: `May Allah have mercy on you
(Yarhamuk-Allah) ';
when he is sick, visit him;
and when he dies, follow his funeral".

Commentary:
The bond of brotherhood among the Muslims has been further strengthened
by the list in this Hadith about the rights of Muslims on one another.