How does a woman determine her purity by dryness or by the white discharge if she is unable to check immediately, and then she sees a yellowish or brownish discharge? Is this yellowish or brownish discharge considered to be after purity, or is menstruation still ongoing?

A woman identifies ritual purity (tahara) by two signs: the discharge of a white secretion (al-qassah al-bayda’) or complete dryness. She should check for her purity before sleep and at prayer times.

If a woman doubts her purity, the default is that menstruation persists, and she should not rush until she sees the sign of purity.

She is not required to constantly check, but rather to look at prayer times and before sleep. If she makes a mistake in estimating purity, there is no sin upon her. She should make up for missed fasting if there was an error, and make up for missed prayers as a precaution if she had left them, thinking she was menstruating, but then it became clear she was pure.