On the Genealogy of Morality (Chap. 3.25) Friedrich Nietzsche

But what am I talking about here? Enough, enough! At this stage there’s only one thing appropriate for me to do: keep quiet. Otherwise, I’ll make the mistake of arrogating to myself something which only someone younger is free to do, someone “more of the future,” someone more powerful than I am—something which only Zarathustra is free to do, Zarathustra the Godless . . . .*

Zarathustra: a name for the Persian prophet Zoroaster, which Nietzsche appropriates to designate a spokesman for his own ideas.