Once every thousand years a little bird comes to this rock to sharpen its beak (idea)

From Hendrik Willem van Loon's History of Mankind (published 1922), a version of the full quotation:

High in the North in a land called Svithjod there is a mountain.
It is a hundred miles long and a hundred miles high
and once every thousand years a little bird comes to this mountain to sharpen its beak.
When the mountain has thus been worn away a single day of eternity will have passed.