Do not have sexual relations with your wife's sister

'You shall not marry a woman in addition to her sister as a rival while she is alive, to uncover her nakedness.

Hebrew

יח וְאִשָּׁה אֶל-אֲחֹתָהּ, לֹא תִקָּח: לִצְרֹר, לְגַלּוֹת עֶרְוָתָהּ עָלֶיהָ--בְּחַיֶּיהָ.

Greek

18 γυναῖκα ἐπὶ ἀδελφῇ αὐτῆς οὐ λήμψῃ ἀντίζηλον ἀποκαλύψαι τὴν ἀσχημοσύνην αὐτῆς ἐπ᾿ αὐτῇ ἔτι ζώσης αὐτῆς.

• Parashah: Acharei Mot
• Sefer HaChinuch: 206
• Mishneh Torah: Holiness — Forbidden Sexual Relations

• Leviticus 18:18

Enumeration and classification from BibleData. The Greek is the Septuagint reading of the same verse, carried by the source for comparison.