Musannaf Ibn Abi Shayba 27:587

'Abdullah ibn Idris narrated to us, from al-Hasan ibn 'Ubaydullah, from Ibrahim ibn Suwayd, from 'Abd al-Rahman ibn Yazid, from 'Abdullah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said to me: "Your permission [to enter] is that you lift the curtain and that you listen to my private conversation until I forbid you."