Musannaf Ibn Abi Shayba 9:309

Hatim ibn Wardan narrated to us, from Burayd, from al-Zuhri, who said: Whoever possesses the marriage contract of a woman, she becomes forbidden to his son. And whichever of the two [the man or the woman] strips [the other] and looks at the private part, it is the same [i.e., it results in the same prohibition].