Is Rubbing Essential in Wudu and Ghusl?
Question

Is it essential to rub the body with the hand when doing Ghusl following a wet dream, or is it sufficient to pour the water over the body?.
Praise be to Allah.Ruling on Rubbing During Wudu and Ghusl
It is not essential to rub the body when doing Wudu or Ghusl, according to the majority of scholars. It is sufficient to make sure that the water reaches all parts of the body in the case of Ghusl. Malik (may Allah have mercy on him) differed with regard to this point.
An-Nawawi (may Allah have mercy on him) said: Our view is that rubbing the parts of the body when doing Ghusl and Wudu is Sunnah, not obligatory. If he pours water over himself and makes it reach every part without touching it with his hand, or he immerses himself in a large amount of water, or he stands beneath a downspout or in the rain with the intention of doing Ghusl, and it reaches his hair and his skin, this is acceptable for Wudu and Ghusl. This is the view of all the scholars, except Malik and Al-Muzani, who stipulated that rubbing the skin is essential for Ghusl and Wudu to be valid.
Our companions quoted as evidence the words of the Prophet (peace and blessings of Allah be upon him) to Abu Dharr (may Allah be pleased with him): “When you find water, let it touch your skin,” but he did not tell him to do anything more than that. This is a sound Hadith, and there are many similar reports in the Hadith.” (End quote from Al-Majmu`,  2/214)
Ibn Qudamah (may Allah have mercy on him) said: He does not have to pass his hand over his body when doing Ghusl or Wudu, if he is certain or thinks it most likely that the water has reached all of his body. This is the view of Al-Hasan, An-Nakha`i, Ash-Sha`bi, Hammad, Ath-Thawri, Al-Awza`i, Ash-Shafi`i, Is-haq and As-hab Ar-Ra’i.
The Maliki View: Rubbing Is Essential for Valid Purification
Malik (may Allah have mercy on him) said: It is obligatory for him to pass his hand over whatever he can reach. Something similar was stated by Abu Al-`Aliyah. `Ata’ said: With regard to the one who is Junub pouring water all over himself, that is not sufficient, rather he should do Ghusl properly, because Allah Says (interpretation of the meaning): {till you wash your whole body} [An-Nisa` 4:43], and the word Ightasal (translated here as “wash your whole body”) refers to one who rubs himself. And because Ghusl is purification from impurity, it is essential to pass the hands over the body, as in Tayammum.
Evidence on Rubbing in Wudu and Ghusl from the Sunnah
There is the report which was narrated by Umm Salamah (may Allah be pleased with her) who said: I said: “O Messenger of Allah, I have braided hair, do I have to do it every time I do Ghusl from Janabah and menstruation?” He (peace and blessings of Allah be upon him) said to her, “Rather it is sufficient for you to pour water over your head three times, then pour water all over your body, and you will be Tahir (pure).” (Narrated by Muslim) (Janabah  is a state of ritual impurity caused by the discharge of semen or sexual intercourse)
Because it is an obligatory Ghusl, it is not essential to pass the hands over the body as in the case of washing off an impure substance. What they have said about Ghusl meaning to pass the hand over something is not sound, because the word Ghasala is used in Arabic to refer to washing a vessel, even if one does not wipe it with the hand.  And the reason why in Tayammum we are commanded to wipe with the hand is because it is purification using dust and it is not possible to make the dust reach the skin without passing the hand over it.” (End quote from Al-Mughni,  1/290)
For more details, please see the following answers: 212399, 90218, 163816, 2648,
And Allah knows best.