It is not permissible to fast during the days of “haiz” (monthly menstrual cycle), or “nifas” (vaginal bleeding that occurs after a woman gives birth to a child). After the bleeding stops and the woman has attained purity, she must perform qaza for the missed fasts.
On the other hand, it is mandatory to fast during “istehaaza” (vaginal bleeding that is neither due to menstruation nor due to giving birth).
۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔
دلائل:
الھندیة: (206/1)
(ومنھا الحیض والنفاس) وإذ حاضت المرأۃ أو نفست افطرت کذا فی الھدایہ۔
Allah the Almighty knows best.
Darul ifta Al-Ikhlas, Karachi.