Is a woman's fast valid if she intended to fast at dawn on the fourth day of her menstrual cycle, believing that her period had ended, even though she had not purified herself, and she fasted the entire day without any blood descending? And is the fifth day considered part of menstruation if a small, light amount of blood descends on it?

For the validity of the fast, a woman must be free from menstruation and postpartum bleeding. If she sees purity (cessation of bleeding) before Fajr and intends to fast, her fast is valid even if she does not perform ghusl until after Fajr, as long as menstruation does not return before fifteen days have passed since her purity. If menstruation returns before fifteen days have passed, she must make up the fasts she observed during that period because she was not considered pure (the "synthesis" school of thought). Some scholars hold that days of menstruation are menstruation and days of purity are purity, and therefore she does not have to make up those fasts (the "patchwork" school of thought). Adhering to the first opinion is more cautious. However, if she does not see true purity (dryness or a white discharge), her fast is invalid.