´It was narrated that 'Abdullah said:` "The Messenger of Allah said to me: 'The sign that you have been permitted to come in is that you raise the curtain and that you hear me speaking quietly, until I forbid you.' (i.e. unless I forbid you)."
Hadith ReferenceSunan Ibn Majah / Chapter: The virtues of the Companions of the Messenger of Allah (saws) / Hadith: 139