How can a woman ascertain her purity, and what is the ruling on her prayer and fasting, if her menstrual period stops for three days and then a brownish discharge and secretions appear, knowing that her period does not have a fixed duration?

A woman knows she has become pure by one of two signs: (dryness or the white discharge). Once she sees either of them, ghusl (definition) becomes obligatory upon her, and she should not wait to see the other. If she sees a yellowish or brownish discharge after achieving purity, then if it is within the period of her regular menses, it is considered menstruation. Otherwise, it is not considered menstruation.