It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that he heard the Noble Prophet (peace and blessings be upon him) saying: A Muslim has five rights over another Muslim: when you meet him, greet him with salam; when he sneezes and says "Alhamdulillah," respond to him; when he is ill, visit him; when he dies, attend his funeral; and when he invites you, accept his invitation.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 10966