Sa'd ibn Abdullah narrated from Ahmad ibn Muhammad, from Muhammad ibn Amr ibn Sa'id Al-Zayyat, from Yunus ibn Ya'qub, who said: I asked Abu Abdillah عليه السلام about a woman who saw blood during her menstrual period, and it exceeded her usual time. When should she start praying? Imam عليه السلام said: "She should consider the number of days she used to sit (for her regular menstruation) and then add a precautionary period of up to ten days. If she sees continuous and heavy blood flow, she should perform ghusl (ritual purification) at the time of every prayer."