سنن ابن ماجه

It was narrated from Abu Mas’ud that the Prophet (ﷺ) said: “The Muslim has four things due from the Muslim: He should answer [by saying Yarhamuk-Allah (may Allah have mercy on you)] to him if he sneezes (and says Al-Hamdulillah); he should accept his invitation if he invites him; he should attend his funeral if he dies; and he should visit him if he falls sick.”