Sahih Muslim #2564

The Prophet (ﷺ) said: 'Allah will say on the Day of Judgment, "O son of Adam, I was ill but you did not visit Me." The man will reply, "O Lord, how could I visit You when You are the Lord of the Worlds?" Allah will say, "Did you not know that My servant so-and-so was ill and you did not visit him? Had you visited him, you would have found Me with him."'