Musannaf Ibn Abi Shayba 35:206

Ibn ‘Uyaynah narrated to us, from al-Zuhri, who heard Sahl ibn Hunayf say: A man peeked through a hole in the chamber of the Prophet, may Allah bless him and grant him peace, while he had a comb with which he was scratching his head. He said: "If I knew that you were looking, I would have thrust it into your eyes. Permission is only for the sake of the sight."