Thick hair is that through which the skin cannot be seen.

The scholars said: With regard to purifying hair and what lies beneath it, it falls into three categories (1):

First: that whose outer and inner parts must be purified in all circumstances. This applies to obligatory ghusl.

Second: that whose outer and inner parts must be purified if it is thin, while only its outer part must be purified if it is thick. This applies to wudu.

Third: that whose inner part need not be purified, whether it is thick or thin. This applies to tayammum.

The evidence that this ghusl is sufficient is Allah’s statement, Exalted is He: “If you are in a state of major ritual impurity, then purify yourselves.” [al-Ma’idah 5:6] Allah mentioned nothing beyond this; whoever washes his entire body once may rightly be described as having purified himself.

If it is said: This verse is general, and the Prophet, peace and blessings be upon him, explained this generality through his practice; thus, it becomes obligatory to perform ghusl in the manner in which he used to perform it—just as, when Allah said, “Establish the prayer,” [al-Muzzammil 73:20] the Prophet, peace and blessings be upon him, explained this establishment through his practice, so that it became obligatory for us to establish the prayer as the Messenger, peace and blessings be upon him, performed it.

The response is from two angles:

First: Had Allah intended us to perform ghusl in a detailed manner, He would have explained it, just as He explained wudu in detail. Since He stated ghusl in general terms . . .