It wasnarrated from Abu Mas'ud that the Prophet (ﷺ) said:
"TheMuslimhas four things due from the Muslim: He should answer [bysayingYarhamuk-Allah (may Allah have mercy on you)] to him if hesneezes(and says Al-Hamdulillah); he should accept his invitation ifheinvites him; he should attend his funeral if he dies; and he shouldvisit him if he falls sick."
English reference: Vol. 1, Book 6, Hadith 1434
Arabic reference: Book 6, Hadith 1501