If a man lies with a menstruating woman and has sexual relations with her, he has exposed the source of her flow, and she has uncovered the source of her blood. Both of them must be cut off from among their people.
KJV
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.
ASV
And if a man shall lie with a woman having her sickness, and shall uncover her nakedness; he hath made naked her fountain, and she hath uncovered the fountain of her blood: and both of them shall be cut off from among their people.