Is it permissible for a woman in postpartum bleeding (nifas) to fast if her bleeding has stopped and she will complete the forty days on the 5th of Ramadan?

If a woman in puerperal bleeding (nifas) ascertains purity before the forty-day period, she is obligated to perform what is incumbent upon other women who are not in nifas, such as prayer and fasting, and she should not wait until the completion of forty days.