Is it possible for the period of menstruation to shorten, or is it fixed? Is it permissible for a husband to have intercourse with his wife if the menstrual bleeding stops and she sees the sign of purity, then the blood returns again after intercourse? What is the sign of purity for a woman? And what should she do? And what should she do if her husband has intercourse with her and then menstrual blood comes down immediately after intercourse?

If a woman experiences the cessation of her menstrual bleeding and sees the sign of purity after five days, while her usual period is seven days, she is considered pure. Prayer becomes obligatory upon her, and her husband is permitted to have intercourse with her. She is not required to wait for the completion of seven days. If the bleeding returns during the menstrual period, it is considered menstrual blood, and there is no sin upon them for the intercourse that occurred during the period of valid purity. However, if menstrual blood appears during intercourse, it must be stopped immediately. The sign of purity is recognized either by dryness or by the emission of white discharge (al-qassah al-bayda').