Deuteronomy 7:3; Deuteronomy 27:23

Deuteronomy 7:3

3 Neither shalt thou make marriages with them; thy daughter thou shalt not give unto his son, nor his daughter shalt thou take unto thy son.

Deuteronomy 27:23

23 Cursed be he that lieth with his mother in law. And all the people shall say, Amen.