Is it obligatory to run water through the hair and wash behind the ears and under the armpits in a sufficient ghusl, or is a quick wash enough? And are the prayers valid if the washing of these areas was forgotten? What is the ruling on the presence of a water barrier, whether little or much, after performing ghusl or after performing the prayers?

In ghusl, water must cover the entire outer surface of the body and reach the roots of the hair. Care must be taken to ensure water reaches areas that are not easily accessible, such as the navel, the inside of the ears, and between the buttocks. Overcoming doubt about covering the body with water is sufficient, and doubt after completing ghusl does not affect its validity.

If one becomes certain that they missed washing a required part, their purification is invalid, and they must wash the missed part and repeat the prayers they performed with that purification.

As for anything that prevents water from reaching the skin, it invalidates ghusl according to the majority of scholars, whether it is little or much. If a barrier is found after ghusl, it must be removed, the area beneath it washed, and the prayers performed before its removal repeated. It is not necessary to repeat the entire ghusl because continuous succession (muwalat) is not a condition. If there is doubt about when the barrier was present, it is attributed to the latest possible time it could have existed.