Leviticus 18:17-18

¹⁷The nakedness of a woman and her daughter shall you not uncover; her son's daughter, and her daughter's daughter, shall you not take, to uncover their nakedness, for they are your kinswomen: it is impiety.

¹⁸You shall not take a wife in addition to her sister, as a rival, to uncover her nakedness in opposition to her, while she is yet living.