مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3661
Musnad of Abdullah bin Mas'ood
It was narrated that 'Abdullah (رضي الله عنه) said: The Messenger of Allah (ﷺ) said: “Permission to enter upon me will be granted when you lift the curtain and you will be permitted to listen to my private conversation until I tell you not to.”
Musnad Ahmad 3684A saheeh hadeeth; Muslim (2169) this is a da'eef isnad]