What is the established ruling concerning the duration for a beginner (Mubtadi'ah) in subsequent months?

Primary text

The explicit ruling for the beginner mandates establishing the pattern through repetition three times. Thus, she should not deviate from certainty in the third month. In the case of a woman with an established cycle who bleeds beyond her cycle, one narration mandates she observes the excess period twice; similarly, the established pattern should be followed here. According to all narrations, if the bleeding ceases at or before the maximum duration, and the duration is consistent over three months, that becomes her established cycle, and she must make up any obligatory fasting performed during that time because it is established that she fasted during her menses.