Musannaf Ibn Abi Shayba 22:397

Abu al-Ahwas narrated to us, from Harun ibn Antara, from his father, who said: I asked Ibn Abbas, "Which deed is best?" He said: "The remembrance of Allah. And no people sit in a house, engaging in the Book of Allah among themselves and studying it, but the angels shade them with their wings, and they are the guests of Allah as long as they remain in it, until they delve into a different conversation."