Imam al-Bukhari (may Allah have mercy on him) said: "Sayyiduna Uthman (may Allah be pleased with him) accepted the invitation of a slave of al-Mughirah bin Shu'bah (may Allah be pleased with him)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / Q20294
Sayyiduna al-Bara' bin Azib (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) commanded seven things: "1. Offering the funeral prayer, 2. visiting the sick, 3. responding to one who sneezes, 4. helping the oppressed, 5. spreading the greeting of salam, 6. accepting invitations, 7. fulfilling oaths."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20294
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
Aswad (may Allah have mercy on him) said that when delegations came to Sayyiduna Umar (may Allah be pleased with him), he would ask them: Does your governor visit the sick? Does he accept the invitation of a slave? What is his conduct? Who stands at his door? If they answered no regarding any one of these qualities, he would remove that governor.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20296