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 6229
Thauban reported Allah's Apostle (may peace be upon him) as saying: Verily, when a Muslim visits his brother in Islam he is supposed to remain in the fruit garden of Paradise until he returns.