"I had two times of visiting the Messenger of Allah(ﷺ), at night and during the day. If I came to him when he was praying, he would clear his throat (to let me know he was praying)."
Sunan Ibn Majah Book 33, Hadith 52
← Previous Hadith "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."

Sunan Ibn Majah Book 33, Hadith 51 Next Hadith → "I asked the Prophet(ﷺ) for permission to enter, and he said: 'Who is that?' I said: 'Me'. The Prophet(ﷺ) said " Me, me?!"

Sunan Ibn Majah Book 33, Hadith 53