Ruling 490

If on two consecutive months a woman with a habit of ḥayḍ – whether it be a habit of time, duration, or both – experiences bleeding that is contrary to her habit and her bleeding in both months is the same in terms of its time, duration, or both, her habit will change to what she has observed in these two months. For example, if she used to experience bleeding from the first day of the month to the seventh and then her bleeding would stop, then in the event that in two consecutive months she experiences bleeding from the tenth to the seventeenth of the month and then her bleeding stops, her habit will change and be from the tenth to the seventeenth.