How can purity and the obligatory prayer be distinguished in the case of an irregular menstrual cycle, where it is strong for two days, then stops for three days, and returns in the form of intermittent spotting that continues for up to ten days?

As long as the total duration of menstruation does not exceed fifteen days, it is considered complete menstruation, and the menstrual cycle may change. As for the three days during which bleeding stops during menstruation, there is a difference of opinion regarding their ruling:

- First Opinion (Shafi'i and Hanafi schools): These days are considered part of menstruation, so there is no prayer or fasting during them. - Second Opinion (Maliki and Hanbali schools): These days are considered a state of purity, and prayer and fasting are obligatory during them.

It is permissible to follow either of the two opinions, with the obligation to make up the prayers in the second opinion for those who did not pray. This is if the cessation is complete; but if there is any trace of blood, it is not considered a cessation, and these days are counted as part of menstruation.