In the name of Allaah, the Most Most Merciful, Bestower of Mercy.
It happens that a woman bleeds from her private parts and falls into doubt with regard to whether it is menstrual blood which forbids her from praying and fasting or non-menstrual bleeding which requires that she continue to pray, fast and have relations with her husband.
She Can’t Tell Whether It’s Menstrual Blood or Not?
Shaikh Ibn ‘Uthaimeen (rahimahullaah) was asked:
If a woman falls into doubt and it is not able to distinguish whether her bleeding is menstrual (hayd) or non-menstrual bleeding (istihaadah), so how is it to be considered?
The origin of blood that exits the private area of a woman is that it is considered as menstrual until it is made clear that it is non-menstrual. So based upon this she is to consider her bleeding as menstrual so long as it is not clear to her that it is non-menstrual.
[Majmoo’ Fataawa wa Rasaa’il of Shaikh Ibn ‘Uthaimeen 4/275]