It is obvious that the common Hobbits (and men) knew nothing of the true nature of the [Istari](https://en.wikipedia.org/wiki/Wizard_%28Middle-earth%29). When the Istari arrived in Middle-earth they were considered "strange elves" (as a matter of fact, Gandalf means "staff elf") or "strange men", wise, long-lived and mysterious, but the treatment that Barliman Butterbur or Denethor gave to Gandalf would have been very different from that which he actually received had it been known that he was a Maia.

But it is clear from the book that Frodo knew the true nature of Gandalf and Saruman. When the Scourging of the Shire, he refers to Saruman as:

> 
> someone of a race against which we would never have dared to raise our hand.
> 
> 
> 

Is there any passage from Tolkien's books, or other writings, that allows us to know when this was revealed to Frodo (or Bilbo)?