What is the ruling on blood that appears one day after the cessation of menstruation, and is it considered menstrual blood? And what is the ruling on missed prayers if the duration [of menstruation] was incorrect? And is the previous duration of menstruation relied upon in the Shafi'i school of thought?

A woman must perform ghusl (ritual bath) and pray upon seeing purity, indicated by one of its two signs: dryness or the white discharge (al-qassah al-bayda'). If blood reappears during the expected menstrual period, the woman is considered menstruating again, and she must re-perform ghusl after it ceases. The entire duration of blood discharge during the menstrual period is considered menstruation, regardless of the characteristic of the returning blood. This is the fatwa adopted by the Shafi'is. The woman must make up the prayers she missed if she missed them during a period when prayer was obligatory upon her, and she must make up the fasts she broke in all circumstances.