עֶרְוַ֥ת כַּלָּֽתְךָ֖ לֹ֣א תְגַלֵּ֑ה אֵ֤שֶׁת בִּנְךָ֙ הִ֔וא לֹ֥א תְגַלֶּ֖ה עֶרְוָתָֽהּ׃ (ס)
Targum Jonathan on Leviticus
The nakedness of thy daughter-in-law thou shalt not dishonour; she is the wife of thy son, thou shalt not dishonour her nakedness.