Midrasch zu Wajikra 20:14

6) R. Elazar says: Whence is it derived that he (one who is promiscuous) is as guilty before the L–rd as one who lives with a woman and with her mother? It is written here "zimah," and elsewhere (Jeremiah 20:14) "And a man, if he takes a woman and her mother, it is zimah" — whereby we are taught that he is as guilty before the L–rd as one who lives with a woman and with her mother.

12) (Vayikra 20:14) ("And if a man takes a woman and her mother, it is lewdness (zimah). In fire they shall be burned, he and they, and there shall not be lewdness in your midst.") "And a man": to exclude a minor. "if he takes a woman and her mother": In all instances (of ervah), "lying" is written, and here "taking" is written, to teach that he is liable (for ervah) only by way of (previous) taking (in marriage) — whence they ruled: One may marry (the close kin) of a woman that he has forced or seduced; but one who forces or seduces (the close kin) or a woman he has married is liable.

41) (Vayikra 10:6): "and your garments you shall not rend and you will not die." The negative implies the positive (if you do rend them). "and let your brethren, the entire house of Israel, mourn the burning that the L–rd has burned": "burning" is mentioned here, and "burning" is mentioned in respect to (fornication with) a woman and with her mother (Vayikra 20:14) and in respect to the daughter of a Cohein (Vayikra 21:9). Just as the "burning" here is burning of the soul with the body remaining intact, so the "burning" there is burning of the soul with the body remaining intact.