Do drops of blood after the cessation of postpartum bleeding by two weeks invalidate fasting and prayer, and how can one purify oneself from them?

If a woman sees blood after fifteen days have passed since the cessation of postpartum bleeding (nifas (definition)), then it is menstruation (hayd), and she is obligated to observe all the rulings applicable to a menstruating woman. If she sees it before fifteen days have passed, it is considered nifas blood according to the Shafi'i and Maliki schools, and it is safer to perform ghusl (definition) (ritual bath) and make up for any missed fasting. According to the Hanbali school, this blood is not considered menstruation unless it coincides with her usual cycle; otherwise, she should purify herself for each prayer, perform the prayer, and her fast is valid.