What is the obligation regarding making up missed fasts if a woman used the minimum period (three days) when her actual cycle was longer (five days)?
Chapter on Menstruation
Al-Mughni
Book of Purification
Primary text
If a woman observes three days of cessation during Ramadan when her actual period was five days, she must make up the five missed days of fasting. This is because the obligation to fast remains upon her, and the two days she refrained from fasting cannot be confirmed to have discharged her religious duty, thus remaining upon the original ruling.
Supporting text
An alternative opinion suggests that three ghusls may be required each month: one after the third day, one after the fourth, and one after the fifth, arguing that a ghusl is necessary after the fourth day in one of the cycles, and every month is potentially the one requiring purification after the fourth day, similar to the obligation after the fifth day.