Leviticus 20:18

And if a man shall lie with a woman having her sickness, and shall uncover her nakedness; he hath discovered her fountain, and she hath uncovered the fountain of her blood: and both of them shall be cut off from among their people.

Cross-references

Leviticus 15:24 describes uncleanness from sex during menstruation; this verse gives the penalty of being cut off.

Leviticus 18:19 prohibits sex during menstruation; this verse states the penalty for that act.

Leviticus 15:19 defines the menstrual impurity that makes the act in this verse a capital offense.

Leviticus 15:33 also forbids lying with a menstruating woman, emphasizing uncleanness rather than the penalty here.

Ezekiel 22:10 names this same sin — humbling a woman during menstruation — as evidence of Jerusalem's moral corruption.