Is it permissible for a disabled person to fast if he is unable to perform ghusl after a state of janabah?

If someone is unable to perform a full ritual bath (ghusl) due to a valid excuse, they must wash whatever part of their body they can, and then perform tayammum (dry ablution) for the parts they are unable to wash. If they are unable to wash any part of their body, then tayammum suffices, as Allah Almighty says: "And if you find no water, then perform tayammum with clean earth." Once their purification is complete, there is no blame upon them regarding fasting, because ritual impurity (janabah) does not affect the validity of the fast, especially when its ruling is lifted by tayammum.