What is the ruling on the fast of a woman who underwent a surgical procedure on her reproductive system, and bled for several days, and she fasted based on the doctor's statement that she was permitted to fast?

The blood discharged from a woman is either menstrual blood or post-partum bleeding (nifas (definition)). Fasting is invalid with either of these, by scholarly consensus, due to the Prophet's (peace and blessings be upon him) saying: "Is it not that when she menstruates – meaning the woman – she neither prays nor fasts?"

Alternatively, it may not be menstrual blood or post-partum bleeding, such as blood discharged due to a hemorrhage or a surgical operation. This type of blood does not prevent prayer or fasting. Rather, the woman is considered pure and should perform ablution for each prayer after its time has begun, based on the Prophet's (peace and blessings be upon him) saying concerning the woman with irregular bleeding (mustahada): "That is but a vein, and not menstruation." Accordingly, her fast is valid.