“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.”
King James Version (KJV)
20:17 See her nakedness - In this and several of the following verses, uncovering nakedness plainly appears to mean not marriage, but fornication or adultery.
20:20 They shall die childless - Either shall be speedily cut off ere they can have a child by that incestuous conjunction; if this seem a less crime than most of the former incestuous mixtures, and therefore the magistrate forbear to punish it with death; yet they shall either have no children from such an unlawful bed, or their children shall die before them.