What is the ruling on the fasting of a woman whose menstrual period continues for 20 days or more?

Scholars have differed in determining the minimum and maximum duration of menstruation (hayd). Sheikh al-Islam Ibn Taymiyyah chose not to specify a time limit for either its minimum or maximum, due to the absence of any evidence from the Quran, Sunnah, or the consensus of scholars indicating such a limit. Therefore, if menstrual bleeding, with its characteristics, continues for twenty days or more, as long as it does not last the entire month, she is considered to be menstruating (ha'id). She should abstain from prayer and fasting, and make up for the fasting once she becomes pure.