What is the ruling on the fasting and prayers of a woman who suffers from continuous vaginal bleeding due to uterine fibroids and is receiving treatment that prevents menstruation, knowing that the bleeding sometimes stops and returns with exertion?

If the "Lupron" injections cause bleeding, the default assumption is that it is menstrual blood. If the bleeding exceeds fifteen days without observing purity, the excess blood is considered istihadah (non-menstrual vaginal bleeding), and you must perform ghusl (ritual bath) and pray. Then, in the following month, you should observe your previous customary period, or differentiate between menstrual blood and istihadah (by color, smell, and pain). If there is no differentiation, you should observe the most common duration of menstruation (six or seven days).

If menstrual blood, with its known characteristics, stops and then reappears, you should fast when it stops and refrain from fasting when it reappears, as the injections might be causing intermittent bleeding.

If the doctor definitively states that the injections completely stop menstruation, then any blood is istihadah, and you must act upon her statement, as ruled by Sheikh Ibn Uthaymeen, may Allah have mercy on him.