Mustadrak al-Hakim — Hadith 1309

Abd al-Rahman bin Abi Layla narrates that Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him) came to visit Sayyiduna al-Hasan bin Ali (may Allah be pleased with them both), and Sayyiduna Ali (may Allah be pleased with him) asked him: "Have you come to visit the sick, or have you come to gloat out of enmity?" He said: Rather, I have come to visit the sick. Sayyiduna Ali (may Allah be pleased with him) said: "If you have come to visit the sick, then listen: I heard the Messenger of Allah (peace and blessings be upon him) saying: Whoever goes to visit his brother is among the picked fruits of the gardens of Paradise; when he sits down, mercy covers him; if it is the morning, seventy thousand angels pray for him until the evening, and if it is the evening, seventy thousand angels pray for him until the morning."
This hadith is sahih (authentic) on the condition of the two Shaykhs, but they did not record it because of a disagreement concerning al-Hakam bin Utaybah.