The idea belongs to Kant, though he arrived at it late and stated it more than once. See Kant for the version that actually gets quoted, and the Groundwork for the argument around it.
The third is usually skipped. Hegel thought the whole thing was empty, and that objection has never fully gone away.
Nothing here links to Nietzsche On Kant yet, which is exactly the kind of gap a seed page is meant to hold open.