All perfect praise be to Allaah, the Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
If the menstruating woman becomes pure before dawn, she must fast that day as we previously stated in Fatwa 40061.
If you did not know that you had become pure and relied on your normal period of menstruation, we hope that you would not incur any sin, Allaah willing, because you were not inclining to sin; you acted upon what you thought to be most likely. If you realized that you had become pure of menstruation during the day, then you should have made Ghusl (ritual bathing) immediately and resumed fasting for the rest of that day. After that, you should have made up for that day without offering expiation. For us, the preponderant opinion is that expiation is obligatory for breaking the fast by having intercourse only, and this is the opinion of the majority of scholars.
Even scholars such as the Maaliki scholars, who consider the expiation obligatory for breaking the fast by something other than intercourse, do not require expiation in this case because the condition of expiation is deliberately violating the sanctity of the month and the absence of misunderstanding. Hence, there is no expiation for breaking the fast of that day, and you are required to make up for it only.