Leviticus 15:19, 25

“Whenever a woman has her menstrual period, she will be ceremonially unclean for seven days. Anyone who touches her during that time will be unclean until evening.

“If a woman has a flow of blood for many days that is unrelated to her menstrual period, or if the blood continues beyond the normal period, she is ceremonially unclean. As during her menstrual period, the woman will be unclean as long as the discharge continues.