Is it obligatory for water to reach the roots of the hair (the scalp) when performing ghusl, or is it sufficient for it to reach the inner parts of the hair if it is thick, as stated in "Al-Fiqh 'ala al-Madahib al-Arba'ah"?

The four Madhhabs (schools of thought) agree on the obligation of running water through the hair during Ghusl (definition) (ritual bath) and ensuring it reaches the skin, whether the hair is thin or thick, including the hair of the beard, armpits, and pubic area. Scholars have used as evidence the Hadith (definition) of Asma: "She takes water and purifies herself, performing the purification well or reaching the purification, then pours it over her head and rubs it until it reaches the roots of her hair, then she pours water over her entire body." And the Hadith of Ali: "Whoever leaves a hair's breadth of janabah (definition) (state of impurity) untouched by water, Allah will deal with him in the Fire in such and such a way." As for Wudu (ablution), it is sufficient to wash the surface of a thick beard, and running water through it is sunnah (definition) (recommended), but it is not obligatory to ensure water reaches the skin beneath it. If the hair is braided with three or more strands, it is not obligatory to unbraid it. However, if the strands are fewer than three, it must be unbraided if it is tightly braided and water cannot reach the skin.