Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "A Muslim has six rights over a Muslim." It was asked: What are they? He (peace and blessings be upon him) said: "1. When you meet your Muslim brother, greet him with salam; 2. when he invites you, accept; 3. when he seeks your sincere advice, advise him sincerely; 4. respond to his sneeze; 5. when he falls ill, visit him; 6. when he dies, attend his funeral prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20295