Musnad Ahmad 5:51

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Al-Hakam ibn 'Utaybah, from 'Abd al-Rahman ibn Abi Layla, who said: Abu Musa came to Al-Hasan ibn 'Ali to visit him. 'Ali said to him: "Have you come as a visitor or as one gloating?" He said: "No, rather as a visitor." 'Ali said to him: "If you have come as a visitor, then I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'When a man visits his Muslim brother, he walks among the plucked fruits of Paradise until he sits. When he sits, mercy envelops him. If it is morning, seventy thousand angels pray for him until evening, and if it is evening, seventy thousand angels pray for him until morning.'"