How much blood invalidates fasting or prayer?

If blood comes from a place other than the vagina, such as a nosebleed, it does not invalidate the fast. As for prayer, there is a detailed ruling regarding its invalidation by emitted blood. If the question is about menstrual blood, the Maliki school holds that there is no minimum limit for it. According to the Shafi'i and Hanbali schools, the minimum is one day and one night or one day. According to the Hanafi school, the minimum is three days.