Sahih Muslim
The Book on General Behaviour (Kitab Al-Adab)
Book Number: 025 / Hadith Number: 5371
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: If a person were to cast a glance in your (house) without permission, and you had in your hand a staff and you would have thrust that in his eyes, there is no harm for you.