Musnad Ahmad 26:137

Waki’ narrated to us, Sufyan narrated to us, from al-Hasan ibn ‘Ubayd Allah, from Ibrahim ibn Suwayd, from ‘Abd Allah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Your permission to enter upon me is that you lift the curtain and that you listen to my private talk (sawadi), until I forbid you." Abu ‘Abd al-Rahman said: My father said: "Sawadi: my secret." He said: He gave him permission to hear his secret.