«خمس من حق المسلم على المسلم: رد التحية وإجابة الدعوة وشهود الجنازة وعيادة المريض وتشميت العاطس إذا حمد الله»
The Prophet (peace and blessings be upon him) said:
"A Muslim has five rights over a Muslim: returning his greeting, accepting his invitation, attending his funeral, visiting him when he is ill, and responding to him when he sneezes and says Alhamdulillah."
Hadith Referenceصحیح الجامع الصغیر / حرف الخاء / 3251