The ruling on the fasting of a menstruating woman if she becomes pure before the dawn

Question: If a menstruating woman becomes pure before the dawn and performs the ritual bath, what is the ruling?

Answer: Her fast is valid if she is certain of her purity before the dawn breaks. The important thing is that the woman is certain that she has become pure; because some women think they have become pure when they have not. For this reason, the women used to bring cotton to Aisha (may Allah be pleased with her) to show it to her as a sign of purity, and she would say to them: Do not hasten until you see the white thread.
So the woman must be careful until she is certain that she has become pure. If she becomes pure, she must intend to fast. Even if she does not perform the ritual bath until after the dawn breaks, she must also pay attention to the prayer and hasten to perform the ritual bath so that she can pray the Fajr prayer in its time. It has reached us that some women become pure after the dawn breaks and before the dawn breaks, but they delay the ritual bath until after the sun rises, claiming that they want to perform a more complete, cleaner, and purer bath. This is a mistake, whether in Ramadan or otherwise; because it is obligatory for her to hasten and perform the ritual bath to pray the prayer in its time. Then she may limit herself to the obligatory bath for performing the prayer. If she wishes to increase her purity and cleanliness after the sun rises, there is no blame on her.
And like the menstruating woman is the one who is in a state of major ritual impurity and does not perform the ritual bath until after the dawn breaks; there is no blame on her and her fast is valid. Similarly, if a man is in a state of major ritual impurity and does not perform the ritual bath from it until after the dawn breaks while he is fasting, there is no blame on him in that; because it is established from the Prophet (peace and blessings be upon him) that the dawn would overtake him while he was in a state of major ritual impurity with his wife, and he would get up and perform the ritual bath after the dawn breaks. And Allah knows best.