Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) transmits this saying of the Prophet (peace and blessings be upon him): "A Muslim is the brother of a Muslim; he does not wrong him and he does not forsake him." The Prophet (peace and blessings be upon him) also said: "By the One in whose Hand is my soul, whenever two people love one another, separation between them occurs only because of a sin that one of them has committed." The Prophet (peace and blessings be upon him) also said: "A Muslim has a right over his brother that he show him six kinds of kindness: when he sneezes, he responds to his sneeze; when he is ill, he visits him; when he is absent, he wishes him well; when he is present and he meets him, he greets him with salam; when he invites him, he accepts; and when he dies, he follows his funeral."
Ahmad recorded it, and its chain is hasan (good).