The Difference Between Menstrual Blood and Irregular Non-Menstrual Bleeding

Question:
How does a woman distinguish between the blood of her regular period and the blood of irregular non-menstrual bleeding?

Answer:
If she becomes pure from her menstruation and then experiences yellowish or brownish discharge afterward, that is irregular non-menstrual bleeding. If the blood occurs during the time of her regular period, it is menstruation, even if it is yellowish or brownish discharge during the time of menstruation. If her menstruation continues, for example, if her usual period is seven days but it continues until ten days, there is no harm in her sitting [not praying], rather it is obligatory for her to sit and not pray or fast; rather, she leaves off the prayer. This is because the regular period increases and decreases up to fifteen days, so its maximum is fifteen days. If her usual period is seven days and then it increases in some instances, and the blood lasts eight, nine, or ten days, there is no harm. She does not pray, does not fast, and her husband does not approach her.
As for if she becomes pure from her menstruation and then sees yellowish or brownish discharge on the days of purity, there is no obligation upon her; she prays and fasts, and there is no obligation upon her. However, she performs the ablution for every prayer. This is based on the saying of the Prophet (peace and blessings be upon him) to the woman with irregular bleeding: , and based on the saying of Umm Atiyyah (may Allah be pleased with her): "We did not consider the brownish or yellowish discharge after purity to be anything." Umm Atiyyah was a Companion who said: "We did not consider the brownish or yellowish discharge after purity to be anything," meaning that only the ablution is required.