I have occasionally wondered whether Frank Herbert might have been influenced by Eric Frank Russell.
In The Great Explosion, reference is made to
followers of a crank named Kassim who tried to unite Mohammedanism and Buddhism by claiming to be the reincarnation of the Prophet of Allah
It is noted that
The Moslem world gave them a rough time until they emigrated.
If I remember correctly, The Great Explosion was published shortly before Dune. Is there any evidence that this notion might have influenced Herbert when he created his Buddhislamic and Zensunni faiths?