My father, may Allah سبحانه وتعالى have mercy on him, wrote to me in his letter: 'Know that the minimum days of menstruation are three days, and the maximum is ten days. If a woman sees blood for three days or more, up to ten days, it is considered menstruation, and She must refrain from prayer and not enter the mosque except while passing through. It is obligatory for her to perform wudu (ablution) before each prayer, sit facing the Qiblah, and remember Allah سبحانه وتعالى for the duration of her daily prayer. If She sees blood for one or two days, it is not considered menstruation unless She sees blood for three consecutive days. She must make up the prayers that She missed during those one or two days. If She sees blood for more than ten days, She should refrain from prayer for ten days, then perform ghusl (ritual bath) on the eleventh day and use a cotton pad (Kersaf). If the blood does not soak through the pad, She can perform her prayers with wudu. If the blood soaks through the pad but does not flow, She prays the Salat Al Layl prayer and the Fajr prayer with ghusl, and the other prayers with wudu. If the blood flows, She prays the Salat Al Layl prayer and the Fajr prayer with ghusl, and the Dhuhr and Asr prayers with ghusl, delaying the Dhuhr prayer slightly and hastening the Asr prayer, and She prays the Maghrib and Isha prayers with one ghusl, delaying the Maghrib prayer slightly and hastening the Isha prayer until her menstruation days arrive, at which point She refrains from prayer. Once She has performed ghusl as described, it becomes permissible for her husband to approach her. The minimum period of purity (tuhr) is ten days, and there is no maximum limit. A menstruating woman should use nine ratls of water for ghusl, measured by the Medinian Ratl. If a woman sees yellowish discharge during her menstruation days, it is considered part of her menstruation. If She sees it during her purification days, it is considered a sign of purity.