Hadith No: 1
Al-Bayhaqi - Sunan al-Kubra - Book of Marriage
The Main Chapters on Encouragement in Marriage and Other Matters
Chapter on What Has Been Reported About a Man Looking at the Nakedness of Another Man and a Woman Looking at the Nakedness of Another Woman, with Each One Being Exposed to the Other
Volume: (7) - Page Number: (159)
13566 - Abu Zakariya ibn Abi Ishaq narrated to us, saying: Abu al-Abbas al-Asamm narrated to us, saying: Bahr ibn Nasr narrated to us, saying: Ibn Wahb narrated to me, from Abd al-Rahman ibn Sulayman, from Amr, the freed slave of al-Mutalib,
from al-Hasan, who said: "It has reached me that the Messenger of Allah (peace be upon him and his holy progeny) said: 'May Allah curse the one who looks and the one who is looked at.'" This is a marshall hadith, and Allah, the Most Knowing, knows best.