Answer: Wiping is only prescribed when there is a covering in place, as we have explained. Thus, if the limb is in a cast, wiping over it is sufficient and no dry ablution is required for that limb.
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Ablution for one afflicted with paralysis
Question: Allah has tested me with paralysis of the lower half of my body, from the waist down to the feet. How am I to perform ablution for the prayer when most of my body is paralyzed? Whenever I need to perform the ritual bath it is extremely difficult, and most of the time I have no one to bring me water or to wash me or help me perform ablution. I am currently praying without ablution. Please guide me—may Allah reward you with every good—are my prayers valid or not, and what do you advise me to do?

Answer: If you are able to perform ablution, even with assistance, then you must do so, even if that means asking someone to bring you water and pour it over your limbs. If you are unable to manage that, it is sufficient for you to perform dry ablution with clean earth. Keep some pure soil near you; when the time for prayer comes and there is no one to help you make ablution or bring you water, perform dry ablution with that soil and pray according to your condition. Allah knows best.

Question: If he can wash some of the limbs but not others, is he required to wash those limbs in addition to performing dry ablution?

Answer: If he can wash some of the limbs but is unable to wash the rest, he washes whatever he is able and performs dry ablution for the remainder.