Deuteronomy 27:23
Cursed be he that lieth with his mother in law. And all the people shall say, Amen.
Cross-reference
Leviticus 20:14
Parallel
In Leviticus 20:14, marrying a woman and her mother is declared wicked — the same sin cursed here, with specified punishment.
Leviticus 18:17
Parallel
In Leviticus 18:17, sexual relations with both a woman and her daughter are forbidden, related but not identical to mother-in-law.