Is light blood, which does not possess the usual characteristics of menstrual blood and which precedes the actual menses, considered menstruation, and does one have to stop praying because of it?

The default assumption for blood seen by a woman is that it is menstrual blood until proven to be istihadah (non-menstrual bleeding). Therefore, whenever a woman sees blood at a time suitable for menstruation, she abstains from fasting and prayer. This is if she sees it after 13 days or more from the previous menstruation, and the total of its days, including any intermittent purity, does not exceed 15 days.

If the blood – along with any intermittent purity – exceeds 15 days, it becomes clear that she is a mustahadah (a woman experiencing istihadah). In this case, she reverts to her previous habit. Otherwise, she acts according to sound differentiation: this means the blood has the characteristics of menstrual blood in terms of its color, odor, and thickness, and its duration is not less than one day and one night, nor more than 15 days. Any bleeding outside of this is istihadah. She then performs one ghusl (ritual bath) after the end of the menstruation period, and performs ablution for each prayer after its time has begun, taking precautions, and then prays.