Question: When performing an ablution or a ghusl, if one forgets to wash any limb and remembers it after the ghusl or ablution or a few days later, what should one do then?
ANSWER
When one remembers it, it suffices to wash only that part. But if one imitates the Mâlikî Madhhab, when one remembers having forgotten to wash that limb, it is necessary to wash that part right away. It is not necessary to make iâda [to perform a namâz for the second time for any reason whatsoever] of those namâzes that one has performed. If people doubt whether they washed a particular place or not, it is a waswasa, and they do not have to wash that part.

After performing a ghusl, if one sees a waterproof substance, such as some adhesive, on any part of the body, it is enough to remove that substance and wash under it. A new ghusl is not necessary. The situation is also as such in the Mâlikî Madhhab.