Is it necessary to wash all of the hair, even if it is braided and long, in the case of major impurity?
Question

                If a woman is in a state of janaabah and her hair is braided and long, and she takes a handful of water and makes it reach all of her head, does she have to wash all of her hair?.
Praise be to Allah.
    What is required when doing ghusl in the case of janaabah is 
    to make the water reach all of the hair, even if it is long. At-Tirmidhi 
    (106) narrated from Abu Hurayrah (may Allah be pleased with him) that the 
    Prophet (blessings and peace of Allah be upon him) said: “Under each hair is 
    janaabah, so wash the hair and clean the skin.” And it was narrated from 
    ‘Ali (may Allah be pleased with him) that the Prophet (blessings and peace 
    of Allah be upon him) said: “Whoever leaves impurity the size of a hair and 
    does not wash it, such and such will be done to him in the Fire because of 
    it.”

    Narrated by Abu Dawood, 217. These two hadeeths were classed 
    as da‘eef (weak) by Shaykh al-Albaani (may Allah have mercy on him). 

    But the report in which these words are attributed to ‘Ali 
    (may Allah be pleased with him) is saheeh. 

    The scholars of the Standing Committee were asked (5/323): 

    Are the woman who has long hair that is not braided and the 
    woman whose hair is braided regarded as the same in the case of ghusl for 
    janaabah, or is it essential to wash the hair completely in either case? 

    They replied: The one who is in a state of janaabah and the 
    one whose period has ended have to make water reach every part of the body 
    and hair with the intention of purifying themselves, whether the hair is 
    long or short, and whether it is braided or not braided. End quote.

    Shaykh ‘Abd al-‘Azeez ibn ‘Abdullah ibn Baaz; Shaykh ‘Abd 
    ar-Razzaaq ‘Afeefi; Shaykh ‘Abdullah ibn Ghadyaan; Shaykh ‘Abdullah ibn Qa 
    ‘ood 

    Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: It 
    is not permissible for her to wash the outer part of the hair only; rather 
    it is essential that the water reach the roots of the hair and the skin of 
    the head (scalp). But if the hair is braided, she does not have to undo it; 
    rather she has to make the water reach every single hair by placing the 
    braid under the water spout and squeezing it so that the water reaches all 
    of the hair. 

    End quote from Majmoo‘ al-Fataawa, 11/163.