What is the difference between washing (ghusl) and wiping (mash), and is it sufficient to pour water on part of a limb and then rub the entire limb with that water, taking into consideration the doubts of waswasa (whispers of the Shaytan) regarding the delivery of water to all parts of the limb during ablution (wudu)?

Rubbing (delk) is not obligatory in ablution (wudu') and ritual bath (ghusl (definition)) according to the majority of scholars. It is sufficient for water to reach the entirety of the body. So, if one pours water over their body and it reaches it without being touched by the hand, it is sufficient. What is obligatory in ablution is to wash the limbs once and ensure that water reaches them, without the need for rubbing, unless water cannot reach without it. In ghusl, the flowing of water is a condition, whereas for wiping (mas-h), it is sufficient to wipe the place with a wet hand without pouring water. Certainty is not dispelled by doubt, so do not pay attention to doubts after completing the act, for that is from the whisperings of Satan.