The ruling on the fasting of a woman whose menstruation stopped and then returned a second time

Question:
In her final question, she says: If a woman’s excuse (menstruation) lasts for four days, then stops, and she takes a bath because she thinks she has become pure, and she fasts for a full day, but the next day the excuse returns to her again, does she have to make up that day or not?

Answer:
She does not have to make up that day, if the blood stopped for her that day and she did not see any blood until after the sun had set, then her fast for that day is valid. The blood that returned to her after that day is considered menstrual blood if it is within the usual number of days of her cycle. As for if it is outside her usual cycle, if her usual cycle is four days and she became pure, then blood came to her after the fifth day in which she had become pure, then there is a distinction here. If it is murky or yellowish, then no action is required regarding it; she prays, fasts, and performs wudu for every prayer. But if it is genuine blood, then it is a continuation of the menstruation, becoming a menstruation following the first one. The day in which she was pure is a valid day, her fast is valid, and praise be to Allah. May Allah reward you with good.