Is blood that flows continuously for more than 15 days, is black in color, and has an unpleasant odor considered menstruation, for which prayer must be stopped, and the husband is prohibited from intimate relations with his wife?

What you did, praying after fifteen days from the onset of bleeding, is correct; because the maximum duration of menstruation is fifteen days, and anything exceeding that is considered istihadah (non-menstrual vaginal bleeding). A woman experiencing istihadah has the same rulings as a ritually pure woman regarding the obligation of prayer and the permissibility of intercourse. However, she must take precautions and perform ablution for every prayer after its time has begun.

To determine the duration of menstruation: 1. If you have a prior established habit: You observe it each month, and anything beyond it is istihadah. 2. If you do not have a prior habit but can distinguish menstrual blood: You observe the duration correctly identified by distinction as menstruation. 3. If you have neither a habit nor the ability to distinguish: You observe six or seven days, as is the common habit of women in your family, and anything beyond that is istihadah.

You are required to make up the prayers missed during the period that exceeded your habit, until the bleeding passed fifteen days. It is permissible for your husband to have intercourse with you during the period of istihadah, after the duration you considered menstruation has ended.