What is the method for washing hair when performing ghusl after menstruation? Is it sufficient to deliver water to the roots of the hair, or must it reach every strand? And is a strong presumption [ghalabat al-ẓann] sufficient in this matter?

It is obligatory to pour water over the head and run it through the roots of the hair until the skin is saturated. A strong presumption of saturation and the water reaching the hair roots is sufficient, without requiring certainty, to avoid obsessive doubt (waswasah).