Musnad Abu Ya'la al-Mawsili 140:55

Ibrahim ibn Muhammad ibn ‘Ar‘arah narrated to us, Yusuf ibn Ya‘qub narrated to us, Maymun ibn ‘Ajlan narrated to us, from Maymun ibn Siyah, from Anas, that the Prophet (peace and blessings of Allah be upon him) said: "There is no Muslim servant who comes to a brother of his, visiting him for the sake of Allah, except that a caller from the heaven calls out to him: 'You have become good, and Paradise has become good for you.' And Allah says in the kingdom of His Throne: 'He visited for My sake, and upon Me is his hospitality; and I am not satisfied for him with any hospitality less than Paradise.'"