It is narrated from Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) that a man peeped through a hole in the door of the Prophet (peace and blessings be upon him), while the Prophet (peace and blessings be upon him) had a comb with which he was scratching his head. So the Prophet (peace and blessings be upon him) said: "Had I known that you were waiting for me, I would have thrust this into your eye. The screen has only been placed for the sake of permission" - or he said: "because of the sight" (the narrator is unsure of the wording).
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5646