What is the ruling regarding someone whose left forearm is disabled, and he is unable to wash his right forearm for ablution?

If you are unable to wash your right forearm with your left forearm, it is sufficient to pour water over the forearm until it is covered, because rubbing (delk) is a recommended act, not an obligatory one, according to the majority of scholars. If you are also unable to do that, then you must seek assistance from men or from your unmarriageable female relatives (mahārim). If you do not find anyone, then wash what you can of the ablution organs and then perform tayammum (definition) (dry ablution) for the forearm that you were unable to wash. This is the view of the majority of scholars, based on the Almighty's saying: "So fear Allah as much as you are able" (Quran 64:16) and "Allah does not burden a soul beyond its capacity" (Quran 2:286). Some scholars hold the view that nothing is required of you if you are unable to wash it, but the first opinion is sounder. If you are also unable to perform tayammum, then nothing is required of you.