Lu'lu' wal-Marjan

Hazrat Sahl bin Sa’d al-Sa’idi (may Allah be pleased with him) reported that a man began to peep through a hole in the door of the Prophet Muhammad’s (peace and blessings be upon him) house. At that time, the Prophet (peace and blessings be upon him) had an iron comb with which he was combing his hair. When he saw the man, he said, “If I had known that you were peeping while waiting for me, I would have poked this into your eye.” Then he said, “The command to seek permission (before entering the house) has been given for this very reason, so that one’s gaze does not fall (inside without permission).”