The Book of Virtue, Good Manners and Joining of the Ties of Relationship (Kitab Al-Birr was-Salat-I-wa'l-Adab)
Muslim :: Book 32 : Hadith 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.