Leviticus 15:19

"And if a woman have an issue, and her issue in her flesh be blood, she shall be in her impurity seven days: and whosoever toucheth her shall be unclean until the even. And every thing that she lieth upon in her impurity shall be unclean: every thing also that she sitteth upon shall be unclean. And whosoever toucheth her bed shall wash his clothes, and bathe himself in water, and be unclean until the even. And whosoever toucheth anything that she sitteth upon shall wash his clothes, and bathe himself in water, and be unclean until the even. And if it be on the bed, or on any thing whereon she sitteth, when he toucheth it, he shall be unclean until the even. And if any man lie with her, and her impurity be upon him, he shall be unclean seven days; and every bed whereon he lieth shall be unclean."

This paragraph deals with the normal menstrual period of women. It is not clear why this period was one in which the woman was considered unclean, and yet commentators tell us that the conviction of this was known universally in all nations prior to the writing of the O.T. Certainly the action of Rachel when hiding the idols from her father Laban indicates that the conviction existed that early, and probably much earlier (Genesis 31:34). Sexual intercourse during a woman's period is expressly forbidden (Leviticus 18:19; Ezekiel 18:6; 22:10).

Note that no sacrifice was required for violations. We appreciate the words of Knight on this Passage:

"Leviticus 15:19 implies that a woman's menstrual period is to be respected ... Here we meet with suggestions about tenderness, affection, and self-control in the married state, and the need for the male to respect the rhythmical cycle of a woman's sexual being."[14]

It is alleged that the sin of David in taking Bathsheba was aggravated "by the fact that she was purifying herself from her uncleanness"[15] (2 Samuel 11:4).