Is it permissible to pray and engage in intercourse after the tenth day of menstruation if its usual duration (7-8 days) has been exceeded and the discharge has become brownish, knowing that the period occurs every 23 days and lasts for more than 11 days?

What a woman sees of brownish discharge mixed with blood is considered menstruation as long as the total duration of blood and the brownish discharge does not exceed fifteen days. In this case, it is not permissible for the husband to have intercourse with his wife until she becomes pure and performs ghusl.