Sayyiduna Sahl bin Sa'd al-Sa'idi (may Allah be pleased with him) says that a man peeped through a hole into his (peace and blessings be upon him) room. He (peace and blessings be upon him) had a comb with which he (peace and blessings be upon him) was scratching his head, and he (peace and blessings be upon him) said: "Had I known that you were peeping, I would have put out your eye. Seeking permission has been prescribed only because of sight."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأشربة والحد فيها / 17651