The Book on Salutations and Greetings (Kitab As-Salam)

Muslim :: Book 26 : Hadith 5393

Ibn Mas'ud reported: The Messenger of Allah (may peace be upon him) said to me: The sign that you have been permitted to come in is that the curtain is raised or that you hear me speaking quietly until I forbid you.

Source materials are from the University of Southern California MSA site
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