Is a woman obligated to fast if she experiences all the signs of menstruation—such as dizziness, lightheadedness, abdominal pain, and seeing blood by inserting a piece of cotton—but the blood does not come out until two or three days later?

The decisive factor in determining a woman to be in her menstrual period is the emission of blood with the characteristics of menstrual blood. If a woman experiences pain or dizziness without the emission of blood, she is not menstruating, and she is obligated to pray and fast. If blood is emitted before sunset, even by five minutes, the fast is invalidated, and that day must be made up. As for a woman inserting cotton before the onset of menstruation, it is not permissible, whereas inserting cotton at the end of the cycle to confirm purity is permissible.