Musnad Ahmad 30:498

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Suhayl ibn Abi Salih, from his father, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever looks into the house of a people without their permission, it has become permissible for them to gouge out his eye."