Sayyiduna Anas (may Allah be pleased with him) narrates this saying of the Prophet (peace and blessings be upon him): "Whenever a Muslim servant goes to visit his brother, and he goes to visit him solely for the pleasure of Allah Almighty, a caller from the heaven calls out to him: 'You have done well, and Paradise has become good for you.' And Allah Almighty says in the dominion of His Throne: 'My servant has gone to visit for My sake; his hospitality is upon Me.'" So Allah Almighty is not pleased to give that person any reward less than Paradise.
Imam al-Bazzar and Imam Abu Ya'la recorded it. The narrators of Abu Ya'la are the narrators of the Sahih, except Maymun bin Ajlan, and he is thiqah (trustworthy).