Sunan Ibn Majah, Volume 5, Book 33, Hadith 3707 (DarusSalam) ⓘ

It was narrated that Abu Ayyub Ansari said: "We said: 'O Messenger of Allah, (we know) this (greeting of) Salam, but what does seeking permission to enter mean?' He said: 'It means a man saying SubhanAllah, and Allahu Akbar and Al Hamdulillah, and clearing his throat, announcing his arrival to the people in the house."

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدُ الرَّحِيمِ بْنُ سُلَيْمَانَ، عَنْ وَاصِلِ بْنِ السَّائِبِ، عَنْ أَبِي سَوْرَةَ، عَنْ أَبِي أَيُّوبَ الأَنْصَارِيِّ، قَالَ قُلْنَا يَا رَسُولَ اللَّهِ هَذَا السَّلاَمُ فَمَا الاِسْتِئْنَاسُ قَالَ ‏ "‏ يَتَكَلَّمُ الرَّجُلُ تَسْبِيحَةً وَتَكْبِيرَةً وَتَحْمِيدَةً وَيَتَنَحْنَحُ وَيُؤْذِنُ أَهْلَ الْبَيْتِ ‏" ‏ ‏.‏