Leviticus 18:19

Also thou shall not approach unto a woman
Not even a man to his own wife, and much less to another woman: to uncover her nakedness, as long as she is put apart for her
uncleanness;
in her monthly courses; and the time of her separation from her husband on that account was seven days, ( Leviticus 15:19 ) ; if a man lay with a woman when in such circumstances, they were both to be cut off from their people, ( Leviticus 20:18 ) ; and such an action is reckoned among sins, and uncleanness of the worst sort, ( Ezekiel 22:10 ) .