“The Muslim has six courtesies due from the Muslim: He should
greet
him with Salam when he meets him; he should accept his
invitation if
he invites him; he should answer [by Yarhamuk-Allah (may
Allah have
mercy on you)] to him if he sneezes (and says Al-
Hamdulillah); he
should visit him if he falls sick; he should follow
his funeral if he
dies; and he should love for him what he loves for
himself.”
Sunan Ibn Majah Book 6, Hadith 1