Is it permissible for a sick person who is unable to perform ghusl after a wet dream, fearing an exacerbation of their illness, to fast in Ramadan?

It is permissible to perform tayammum for prayer if ghusl would exacerbate an illness or delay recovery, based on the Almighty's saying: "And if you are ill or on a journey, or one of you comes from the place of relieving himself, or you have contacted women and find no water, then seek clean earth and wipe over your faces and hands." As for fasting, its validity does not depend on ritual purity, therefore, not performing ghusl from janabah does not affect it.