"Do not have sexual relations with your daughter-in-law. She is your son's wife; do not have relations with her." (NIV)
You shall not uncover the nakedness of your daughter-in-law; she is your son's wife; you shall not have intercourse with her. (AMP)
Thou shalt not uncover the nakedness of thy daughter in law: she is thy son's wife; thou shalt not uncover her nakedness. (KJV)