Ruling on rubbing thick hair when doing ghusl for janaabah

What is
required when doing ghusl is to make the water reach every part of the body.
If it is possible to make the water reach the scalp and go through the hair
and so on, then he does not have to rub it, but if it is not possible to do
that without rubbing it, then he has to rub it. 

What is
required of the one who is doing ghusl is to pour water over all of his hair
and make it reach the roots of his hair, whether his hair is thick or thin.
If he does that then his ghusl is complete. 

It was
narrated from ‘Aa’ishah (may Allah be pleased with her) that she said: When
the Messenger of Allah (blessings and peace of Allah be upon him) did ghusl
for janaabah, he washed his hands and did wudoo’ as for prayer, then he
washed his body, then he ran his hands through his hair, until he was sure
the water had reached the scalp. Then he poured water over his head three
times. Then he washed the rest of his body.

Narrated by
al-Bukhaari, 264 

It says in
al-Mawsoo‘ah al-Fiqhiyyah (13/19): The fuqaha’ are unanimously agreed
that making the water reach all of the hair and skin is one of the
obligatory parts of ghusl. End quote. 

It also says
in al-Mawsoo‘ah al-Fiqhiyyah (26/105): The fuqaha’ are unanimously
agreed that it is obligatory to make the water reach all the hair of the
head, down to the roots, for both males and females. End quote. 

Shaykh
ash-Shanqeeti (may Allah preserve him) said: It is more appropriate to say
that rubbing is not obligatory, but if the water is little, and making the
water reach all of the body can only be done by rubbing, then it is
obligatory in the sense that whatever is essential to doing an obligatory
act is also obligatory. End quote from Sharh Zaad al-Mustaqni‘. 

And Allah knows best.