Musnad Abu Ya'la al-Mawsili 3:29

Zuhayr narrated to us, Abd al-Rahman ibn Mahdi narrated to us, Hammad ibn Salamah narrated to us, from Ya'la ibn 'Ata, from Abdullah ibn Yasar, that 'Amr ibn Hurayth visited al-Hasan ibn 'Ali. 'Ali said to him, "Do you visit al-Hasan while there is in the soul what is in it?" He said, "O 'Ali, you are not the Lord of my heart to turn it wherever you wish." He said, "As for that, it does not prevent me from offering you advice. I heard the Messenger of Allah, may Allah bless him and grant him peace, say: 'There is no Muslim who visits a sick person except that seventy thousand angels pray for him, at whatever hours of the day it may be until he reaches evening, and at whatever hours of the night it may be until he reaches morning.'"