Praise be to Allaah.
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)
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.