Question: We know that menstruation invalidates fasting; and when it endsand a woman has performed Ghusl (ritual bath), then she can resume fasting. She also has to make up for the missed days of fasting. However, there is a woman who performed Ghusl upon noticing that her menstruation blood ceased. But after performing Ghusl, her menstruation restarted again and remained for one more day and stopped. This time she did not perform Ghusl, and yet she fasted for six days after that. Is her fasting for these six days valid or invalid? If it is not valid, is her fasting without performing Ghusl judged as one who does not fast intentionally, bearing in mind that her intention was not to violate the rulings of Islaamic law? If her fasting of those six days is judged like one who intentionally does not fast, and she is poor, then she is obligated to fast for sixty consecutive days. This ruling applies when one does not fast for one day intentionally, then how about missing six days of fasting?
Answer: The menstruating woman is not to perform Ghusl until the bleeding completely ceases and she notices that she is clear from any blood. But, if she performs Ghusl before becoming pure and the complete cessation of blood, and then the bleeding resumes, this blood is considered part of her monthly period, as long as the period of menstruation does not exceed fifteen days. Based on this, the first Ghusl which she performed is not valid, and the day in which the bleeding resumed was part of her monthly period. As such, she had to perform Ghusl after the blood has completely ceased… read more here.