Hadith #3441 (Sunan Ibn Majah)
Book: Etiquette
Narrator(s): al-Walid bin Muslim al-Quraishi الوليد بن مسلم القرشي, Anbasa bin 'Abdur Rahman bin 'Uayna عنبسة بن عبد الرحمن بن عيينة, Muhammad bin Zadhan al-Madni محمد بن زاذان المدني

“We said: ‘O Messenger of Allah(ﷺ), (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.”

Source: https://parallelquran.com/hadith/sunan-ibn-majah-3441/