Musnad Ahmad 32:616

Hassan narrated to us, Hammad ibn Salamah narrated to us, from Thabit al-Bunani, from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The Frequented House (al-Bayt al-Ma'mur) is in the seventh heaven. Seventy thousand angels enter it every day, then they do not return to it."