What is meant by the duration of the menstrual period? Is it only the time during which explicit blood flows, or does it include blood and what is connected to it of turbidity and yellowness? How is the duration of the menstrual period calculated? And is it necessary to perform ghusl and return to a state of purity if the dryness lasts for only one hour?

The intended meaning of "duration of the habit" is the time during which a woman is accustomed to seeing blood. If she sees yellowish or brownish discharge after her habitual period ends, and it is connected to the blood, it is considered menstruation as long as it occurs within the possible duration [of menstruation]. However, if she sees purity (cessation of bleeding) by dryness or by the white discharge (al-Qassah al-Bayda'), and then sees yellowish or brownish discharge after her habitual period has ended, these are not considered menstruation; rather, they fall under the rulings of istihada (non-menstrual bleeding). The dryness considered a sign of purity is confirmed by inserting a piece of cloth into the vagina, and it comes out clean. She must perform ghusl (ritual bath) immediately, even if the period of dryness is only one hour. If she sees blood again after achieving purity, she is considered to have returned to menstruation, as long as the returning blood is within the possible duration of menstruation, and she must repeat ghusl after it stops.