Musannaf Ibn Abi Shayba 30:109

Muhammad ibn Marwan al-Basri narrated to us, from Abu al-Awwam, from Qatadah, from Ibn Abbas: Regarding the saying of Allah, "Fair ones reserved in pavilions" (al-Hur al-maqsurat fi al-khiyam), Ibn Abbas said: The pavilion is a hollowed pearl, a league by a league, in which there are four thousand doors.