Fiqh-us-Sunnah Volume 4, Funerals and Dhikr, Fiqh 4.003A.

Abu Hurairah narrated that the Messenger of Allah, peace be upon him, said: “A caller from heaven calls out to the person who visits a sick person, ‘You are good and your path is good. May you enter your residence in Paradise’.”

Abu Hurairah reported that the Messenger of Allah, peace be upon him, said: “Verily, Allah, the Exalted and Glorious, will say on the Day of Judgement: ‘O Son of Adam! I fell ill, but you did not visit Me.’ The human will ask, ‘O my Sustainer! How could I visit You when You are the Sustainer of the Worlds? And how can You fall sick?’ He, the Almighty, will say, ‘Did you not know that such and such a servant of Mine was sick. But you did not visit him. Did you not know that, had you visited him, you would have found Me by his side? O Son of Adam! I asked you for food, but you fed Me not?’ The man will say, ‘O my Sustainer! How could I feed You when You are the Sustainer of the Worlds? And You are free from hunger?’ He, the Almighty, will say: ‘Such and such a servant of Mine asked you for food, but you refused to give him any. Did you not know that, had you fed him, you would have found it recorded here with Me? O Son of Adam! I asked you for a drink, but you did not give Me any.’ The man will say, ‘O my Sustainer! How could I give You a drink while You are the Sustainer of the Worlds and are free from thirst?’ He, the Almighty will say, ‘Such and such a servant of Mine asked you for a drink, but you did not give him any. Had you given him a drink, you would have surely found that recorded with Me.”‘

Thawban reported that the Prophet, peace be upon him, said: “Verily, when a Muslim visits his sick Muslim brother, he is, as it were, in one of the gardens of Paradise (enjoying its ripe fruits) until he returns to his home.”

Ali said: “I heard the Messenger of Allah, peace be upon him, saying: ‘When a Muslim visits a sick Muslim in the morning, seventy thousand angels pray for him, and they continue praying for him until that evening. When one visits the sick in the evening, the angels pray for him and continue praying for him until the next morning. Moreover, he will be rewarded with the choicest fruits of Paradise.”