How did you ever know that?! (If you recall which book, please let us know!)
I will. I had gone googling for it, but couldn’t find it. I would’ve guessed, “the Book of Jubilees.” Now, I’m wondering if I picked up a a source with a weak argument: I found a passage in Jubilees which describes Mount Zion and the Garden of Eden, from whence waters flowed when Man did have eternal life, as the “navel” of the Earth.
(Who knew Mount Zion was a navel base?)