Is it permissible to fast or must I break my fast if I see hardened blood after my menstrual bleeding has stopped?

A woman recognizes the cessation of menstruation by one of two signs: dryness (inserting a piece of cotton and it comes out clean), or the white discharge (a white fluid). As long as she does not see one of these two signs, she is menstruating, unless the bleeding exceeds fifteen days, in which case she becomes a woman experiencing istihada (non-menstrual vaginal bleeding). This bleeding, about which the question is asked, is menstruation and prohibits fasting and prayer as long as it occurs within a period that is valid for menstruation.