Narrated Abu Huraira Radiallahu Anhu:

I heard Rasulullah Sallallahu Alayhi Wasallam saying, “The rights of a Muslim on the Muslims are five: to respond to the salaam, visiting the sick, to follow the funeral processions, to accept an invitation, and to reply to those who sneeze.

Bukhari Shareef

Narrated ‘Abdullah bin Mas’ud Radiallahu Anhu:

Rasulullah Sallallahu Alayhi Wasallam said: “The blood of a Muslim man, who testifies that none has the right to be worshipped besides Allah, is not lawful except for one of three cases: The married adulterer, a life for a life, and the one who leaves the religion and parts from the Jama’ah (the community of Muslims.)

Tirmidhi Shareef

Narrated Aisha, Ummul Mu’minin Radiallahu Anha:

Rasulullah Sallallahu Alayhi Wasallam said: It is not right for a Muslim to keep apart from another Muslim for more than three days. Then, when he meets him and gives three salutations, receiving during that time no response, the other bears his sin.

Abu Dawood Shareef