He prohibited us from sexual intercourse with a menstruant during the period of her impurity - meaning to say, all of the seven days. And that is His saying, "To a woman, while in her menstrual impurity, you shall not approach to uncover her nakedness" (Leviticus 18:19). [That is] so long as she has not immersed [in a mikveh] after the seven [days]. And one who transgresses this negative commandment volitionally is liable for excision. But [if] inadvertent, he must sacrifice a fixed sin-offering.