Sunan Ibn Majah, Hadith 139 ⓘ
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)."
حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ إِدْرِيسَ، عَنِ الْحَسَنِ بْنِ عُبَيْدِ اللَّهِ، عَنْ إِبْرَاهِيمَ بْنِ سُوَيْدٍ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ يَزِيدَ، عَنْ عَبْدِ اللَّهِ، قَالَ قَالَ لِي رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " إِذْنُكَ عَلَىَّ أَنْ تَرْفَعَ الْحِجَابَ وَأَنْ تَسْمَعَ سِوَادِي حَتَّى أَنْهَاكَ " .
also referenced under: Book 1, Hadith 144 (In-Book) & Volume 1, Book 1, Hadith 139 (DarusSalam)