Leviticus 18:17

“Thou shall not uncover the nakedness of a woman and her daughter, etc.] That is, if a man marries a woman, and she has a daughter, which is the man’s daughter-in-law, after the death of his wife he may not marry this daughter; for this daughter is of the same flesh with her mother, who became one flesh with the man she married, and therefore his relation to her daughter is too near to marry her: Jarchi says, if he does not marry the woman, but only deflower her, it is free for him to marry her daughter; but Aben Ezra says, if he has lain with the mother, the daughter is forbidden; however, if he married either of them, the other was forbidden; he could not marry them both, neither in the…”

“18:17 As with all examples listed in ch 18, marrying a woman together with her daughter or granddaughter was prohibited because of the disruption it would cause in the family order. It would violate the intimacy of the family group by forcing a wife to compete for her husband’s affections against a much younger woman. The penalty for this act was death by burning (20:14).”

“a woman: Lev 20:14; Deu 27:23; Amo 2:7 it is wickedness: Lev 20:14 Leviticus 18:18”

“Marriage with a woman and her daughter, whether both together or in succession, is described in Deu 27:20 as an accursed lying with the mother-in-law; whereas here it is the relation to the step-daughter which is primarily referred to, as we may see from the parallel prohibition, which is added, against taking the daughter of her son or daughter, i.e., the granddaughter-in-law. Both of these were crimes against blood-relationship which were to be punished with death in the case of both parties ( Lev 20:14), because they were "wickedness," זמּה, lit., invention, design, here applied to the crime of licentiousness and whoredom ( Lev 19:29; Jdg 20:6; Job 31:11). Leviticus 18:18”