Leviticus 18:18 KJV
Neither shalt thou take a wife to her sister, to vex her, to uncover her nakedness, beside the other in her life time.
Leviticus 18:16–20 KJV Chapter Context
16
Thou shalt not uncover the nakedness of thy brother’s wife: it is thy brother’s nakedness.
17
Thou shalt not uncover the nakedness of a woman and her daughter, neither shalt thou take her son’s daughter, or her daughter’s daughter, to uncover her nakedness; for they are her near kinswomen: it is wickedness.
18
Neither shalt thou take a wife to her sister, to vex her, to uncover her nakedness, beside the other in her life time.
19
Also thou shalt not approach unto a woman to uncover her nakedness, as long as she is put apart for her uncleanness.
20
Moreover thou shalt not lie carnally with thy neighbour’s wife, to defile thyself with her.