He wants to do ghusl as prescribed in sharee‘ah, using shampoo and soap
Question

                Is it permissible to start ghusl by cleaning oneself with soap and the like, then to do ghusl as prescribed in sharee‘ah?.
Praise be to Allah.
    Using shampoo and soap when doing ghusl as prescribed in 
    sharee‘ah, such as ghusl in the case of janaabah, is not obligatory; rather 
    it is sufficient for the Muslim to pur water over his body so that it 
    reaches every part of it, as we explained in the answer to question no.
    163826. In the answer to 
    question no. 83172 you will 
    find a description of complete and acceptable ghusl. 

    If a person wants to use shampoo and soap when doing his 
    obligatory ghusl, there is nothing wrong with his washing his body with 
    water and shampoo in order to clean it, then doing ghusl as prescribed in 
    sharee‘ah, with water only. There is nothing wrong either with him intending 
    to do ghusl for janaabah with the water with which he is removing the 
    shampoo and soap with which he has cleaned his body, so that he makes water 
    reach his whole body only once, combining the two matters. 

    Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him) 
    was asked: 

    I did ghusl for janaabah using soap and shampoo; does this 
    ghusl count for wudoo’ too, if that was my intention? 

    He replied: That will count for both if you intended both 
    types of purification. But it is preferable to do wudoo’ first, then to do 
    ghusl, as the Prophet (blessings and peace of Allah be upon him) did, 
    because that is more complete. There is nothing wrong with using soap or 
    shampoo or lotus leaves and the like in order to remove dirt. 

    End quote from Fataawa ash-Shaykh Ibn Baaz, 10/173 

    And Allah knows best.