What is the definition of washing in wudu (ablution) and ghusl (bath taken in state of major ritual impurity). I read that it means 'to let water flow over the limb'. What exactly does this mean? Does it mean that you have to let water flow on each and every part of the limb, or does it mean that you must let water flow over the limb once, that any part of the limb is sufficient, and that you can then make the water reach the other parts of the limb by rubbing? Also, what is considered a limb in Ghusl, and which parts can be washed by having water flow and which by rubbing? Please discuss this matter at length so that the issue becomes clear. I saw other questions on your site, but they were not relevant to mine.

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. 

When washing the body parts in Wudhoo' and Ghusl, water must run over them. If a person pours water on part of the body and then wipes the water with his hand over to the rest of it, then this is not sufficient because this is considered wiping and not washing.

Here are some statements of the scholars about this issue:

Al-Baaji from the Maaliki School of jurisprudence, said in Al-Muntaqa:

“Its [washing's] obligation is that the body part must be washed with water by passing the hand, such as scooping the water with his hand, or letting rain water fall on it and so forth. As for wetting one's hand and passing it over the body part that must be washed, then this is not enough because this constitutes wiping and not washing.”

Also, Minah Al-Jaleel, authored by the Maaliki scholar Muhammad 'Ulaysh, reads, “It is a condition that water flows over the body part, from its beginning to its end, and not that water falls from it or drips from it.”

Al-Iqnaa’, authored by Al-Khateeb Ash-Shirbeeni, reads about Ghusl, “In Islamic terminology, Ghusl means that water flows over the entire body, accompanied by the intention (of making Ghusl).”

Haashiyat Ar-Rawdh Al-Murbi’, authored by the Hanbali scholar An-Najdi, reads, “Making the water reach the body part is obligatory according to the consensus of the scholars, and if it is wiping, like if a person pours water on his hands and then he passes his hands on his face or other body parts, then this is not sufficient. This was reported by Ibn Rushd according to the agreement of the scholars because it constitutes wiping and not washing.”

Based on the above, it is an obligation to let water flow over the entire body when performing Ghusl. As regards Wudhoo', it is obligatory to let water flow on all the body parts that must be washed in Wudhoo', and they are four, and each part has a specified area determined by the scholars as follows:

1- The face: Ibn Qudaamah said about the face, “Washing the face from the hairline to the incline of the jawbone and chin and to the beginning of the ears.”

2- The hands (arms) until the elbows: The fatwa of the Standing Committee for Issuing Fataawa reads, “With regard to washing the hands until the elbows after washing the face in Wudhoo', then one should wash the right arm three times and wash the left arm three times as well, from the fingertips to the elbows, and he should wash each arm separately.”

3- Wiping over the head: As-Saawi says in his Haashiyah (footnote), “The head is from the hairline on the front to the nape on the back of the neck along with wiping over the hair on his temples over the protruding bone in the face...” 

4- Washing the feet: The Maaliki scholar Al-Karashi said, “This is the fourth obligation among the obligations that are agreed upon in the consensus of the scholars; which is washing the feet including the ankles…”

Certainty is not an obligation when pouring water all over the body; rather, if one predominantly thinks that the water reached all his body, then it is enough, as a way of removing hardship. Al-Buhooti said in Kash-shaaf Al-Qinaa’, “In pouring water all over the body, it is enough to predominantly think that water has reached all of the skin, because taking certainty into consideration would be a form of hardship.”

1- With regard to rubbing (the body parts), it is a Sunnah in Wudhoo' and Ghusl, and, according to the view of the majority of the scholars, it is not an obligation. Imaam An-Nawawi said in Al-Majmoo':

“The view of our Mathhab (school of Fiqh) is that rubbing the body parts in Ghusl and Wudhoo' is a Sunnah, and not an obligation. So if a person pours water on his body and the water reaches all of his body without him using his hands (to rub it), or he dives in a large body of water or stands under a pipe of running water or under rain with the intention of Ghusl or Wudhoo' and the water reaches his hair and skin, then his Ghusl and Wudhoo' are sufficient. This was stated by all the scholars with the exception of (Imaam) Maalik and Al-Muzani, as they conditioned rubbing for the validity of Ghusl and Wudhoo'.” 

Allaah knows best.