When does a woman whose menstrual cycle is established (having a fixed habit) treat irregular bleeding as menstruation?
Chapter on Menstruation
Al-Mughni
Book of Purification
Primary text
If a woman has an established menstrual habit ('adah mustaqirrah) and sees blood outside of that habit, she does not count that irregular flow as menstruation until it occurs three times, according to one narration, or two times, according to another. Ahmad, as narrated by Hanbal, stated that if a woman with known days anticipates her period, she is not to regard that flow, but must pray and fast. If it recurs a second time similarly, then it is considered shifted menstrual blood. Another narration from Al-Fadl ibn Ziyad states that the shift only occurs on the third occurrence, whereupon she must cease prayer and fasting. In the narration where she is instructed to pray and fast during the first three irregular occurrences, she must make up any obligatory fasts performed during those times because it becomes clear that the fast occurred during menstruation, and fasting during Hayd is invalid. However, she does not make up missed prayers because a menstruating woman does not make up prayers.
Supporting text
Some narrations suggest that the irregular flow may be counted from the third occurrence. One narration from Hanbal allows for the possibility that the shift is counted from the second recurrence. The majority of narrations attributed to Ahmad consider a repetition of two or three times necessary for any flow outside the established days, whether it occurs before, after, or interrupting the established days. If the shift is established, she adopts the new timing and abandons the first established habit.