If someone take menstruation as istihaza? Or istihaza as menstruation? My problem is that my regular menstruation is only coming for two days and a little black or brown substance come on day three so I am not sure whether I should take my regular menstruation as istihaza or haydh. What will happen if it is haydh and I take is istihaza or if it haydh and I take it as istihaza?

The conditions of hayz is that bleeding has to have continuity for the first three days such that one cannot say they are tahir from bleeding at all even for 10 minutes. It is not necessary for the blood to continuously flow out rather if it is present in the inside that is enough.

To check that, take a piece of cotton and insert it at the mouth of the vagina and stand a bit so the cotton goes a bit up. Then take it out and if it comes out dirty then blood is present on the inside which is sufficient for continuity.

However if the condition of continuity is not met, then you have istihadha. If it is istihadha and you take it as haydh then you have to go back and do qadha of the namaz and fasts missed.