In the month of Ramadan, if a woman’s menstrual bleeding stops after the time of imsak (the time when prohibition on eating and drinking starts), she acts like a fasting person. If her menstruation begins after imsak, she eats and drinks secretly that day. In both cases she has to make up for these fast days later on. However, if a woman begins menstruating before she has performed a fard salat whose time has started, she does not have to make it up later on.
If bleeding stops before the time of imsak and she has only time enough to make a ghusl (purificatory bath) and dress up but not enough also to say “Allahu akbar” before the time of morning salat (salat al-fajr), she fasts that day, but she does not have to make up the night salat (salat al-isha) she missed. But if the time is long enough to say “Allahu akbar,” she will have to make up for it. If bleeding begins before iftar (time for breaking a fast), her fasting becomes invalid, and she has to make up for it after Ramadan. If menstruation begins while performing a salat, her salat becomes invalid.