Sahih Muslim
The Book of Virtue, Good Manners and Joining of the Ties of Relationship (Kitab Al-Birr was-Salat-I-wal-Adab)
Book Number: 032 / Hadith Number: 6227
Abu Rabi' reported directly from Allah's Apostle (may peace upon him) as saying: The one who visits the sick is in fact like one who is in the fruit garden of Paradise so long as he does not return.