Sunan At-Tirmidhi

Narrated Sahl bin Sa'd As-Sa'idi: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