How can a woman know that she has become pure from menstruation, and what are the signs of purity, such as "al-qassah al-bayda' (the white discharge)" and dryness, and is "al-qassah al-bayda'" the wadi (a white discharge that often appears after urination) that comes out after urination?

The "white story" (al-qissah al-bayda'): A thin, white discharge that women recognize as the cessation of menstruation; not all women experience it.

Dryness (al-jufuf): When a woman inserts a piece of cotton into the private area and it comes out clean, with no trace of blood, yellowish discharge, or brownish discharge. White secretions do not negate dryness.

If the blood and what is connected to it, such as yellowish or brownish discharge, stops, then you are pure. If you insert cotton into the private area and find it clean, or with white secretions on it, then you are pure and ritual bathing (ghusl) becomes obligatory for you, while avoiding obsessive doubts (waswas).