Ontological argument parallel

In "God is Not Great" by Hitchens:

"Are there dragons?" she asked. I said that there were not. "Have there ever been?" I said all the evidence was to the contrary. "But if there is a word dragon," she said, "then once there must have been dragons."

He points out that this passage is a fairly parallel argument to that made by Augustine in his argument for god:

1. God is the greatest imaginable being.
2. All else being equal, a being or entity that exists is greater than one that doesn't.
3. Therefore, God exists.

(from Iron Chariots wiki)

Questions from reading "God is not Great", by Christopher Hitchens

p.80

Even what was first known about the comparatively consoling symmetry of the solar system, with its nonetheless evident tendency to instability and entropy, upset Sir Isaac Newton enough to make him propose that god intervened every now and then to put the orbits back on an even keel. This exposed him to teasing from Leibniz, who asked why god couldn't have got it right the first time.

I'm curious where this account comes from. I have looked at various quotes and stories concerning the various Newton-Leibniz (and Newton-Hooke) arguments, but nothing about this particular item has surfaced...