Is it obligatory to get water to the roots of the hair in the washed limbs during wudu'?

What is obligatory in ablution (wudu') is to convey water to all limbs that must be washed. Overcoming doubt suffices for this. For washing the limbs, the flow of water over the limb is a condition. If there is hair on the limb that shows the skin, conveying water to it is obligatory; otherwise, it is recommended. If the hair is thick and covers the skin, washing what is beneath it is not obligatory, but it is recommended to run fingers through it. If it shows the skin, washing both the hair and the skin is obligatory. If some of it is light and some is thick, washing the surface of the thick part and the skin of the light part along with it is obligatory. This applies to the hair of the beard, eyebrows, mustache, and the hair between the lower lip and the chin (anafaqa).