Leviticus 18:17-18

¹⁷Thou shalt not uncover the nakedness of a woman and her daughter; thou shalt not take her son’s daughter, or her daughter’s daughter, to uncover her nakedness; they are near kinswomen: it is wickedness.

¹⁸And thou shalt not take a wife to her sister, to be a rival to her, to uncover her nakedness, besides the other in her life-time.