Sayyiduna Sahl bin Sa'd al-Sa'idi (may Allah be pleased with him) narrates that a man peeped in at the Prophet (peace and blessings be upon him) from behind the curtain of the room, and the Prophet (peace and blessings be upon him) had a comb in his hand. He said to him: "Had I known that this man was looking at me before I reached him, I would have stabbed his eye with the comb. Is seeking permission prescribed for anything other than sight?"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأشربة والحد فيها / 17652