Is it obligatory to make up for fasting the eleventh day, given that menstrual blood flows for the first four days, then stops on the fifth day, and on the sixth day a small amount of blood flows, and on the seventh, eighth, and ninth days something different from menstrual blood flows only during the midday period, and on the eleventh day yellowish discharge appears, and the white discharge (qassah al-bayda') is not seen?

The maximum duration of menstruation is fifteen days according to the majority of scholars, while some scholars hold that there is no maximum limit for it. The signs of purity are: the discharge of a white fluid (al-qassah al-bayḍā’), or complete dryness. The yellowish and brownish discharges that are connected to menstruation are considered part of menstruation, but after achieving purity, they are not to be heeded. If the bleeding stops and complete dryness occurs on the fifth day, she must perform ghusl (ritual bath), pray, and fast. If complete dryness does not occur until the eleventh day, then all of it is considered menstruation, and the yellowish discharge within it is also menstruation. If complete dryness occurs, even if only for a few hours, it is a state of purity requiring ghusl and prayer. Regarding fasting on the eleventh day: if the yellowish discharge occurs after a sign of purity, then her fast is valid; otherwise, it is menstruation, and she must make up for it.