Lev.18.18

Neither shalt thou take a wife to her sister, to vex her, to uncover her nakedness, beside the other in her life time.

Lev.18.18

"Don't marry your wife's sister as a rival wife and have sex with her while your wife is living.

Lev.18.18

Nor shall you take a woman as a rival to her sister, to uncover her nakedness while the other is alive.

Lev.18.18

"Do not marry a woman and her sister because they will be rivals. But if your wife dies, then it is all right to marry her sister.