Jami` at-Tirmidhi Book 42, Hadith 23
that 'Amr bin 'Abdullah bin Safwan informed him, that Kaladah bin Hanbal had informed him, that Safwan bin Umayyah sent him to bring some milk, colostrum, and Daghabis (a type of herb) to the Prophet (ﷺ) while he was in the upper valley. (He said): "I entered upon him without seeking permission nor giving Salam. The Prophet (ﷺ) said: 'Go back and say: As-Salamu Alaykum, may I enter?'" And that was after Safwan had accepted Islam."
that a man peeked in on the Messenger of Allah (ﷺ), in one of the apartments of the Prophet (ﷺ), while the Prophet (ﷺ) had a Midrah (an iron comb) with which he was scratching his head. So the Prophet (ﷺ) said: "If I knew that you were looking then I would have poked your eyes with it. Seeking permission has only been enjoined because of the sight."
"I sought permission to enter upon the Prophet (ﷺ) regarding a debt my father owed, so he said: 'Who is this?' I said: 'Me.' He said: 'Me, me.'As if he disliked that."