So I was googling Chesterfield (his envoy reports exist, but I haven't turned up digitized copies yet), and I found this letter he wrote on December 12, 1730, in which he writes,

The King of [sic!] Prussia in the oath he prepared for the Prince to swallow, among many other things, has made him swear that he will never believe in the doctrine of Predestination! A very unnecessary declaration in my mind for any body who has misfortune of being acquainted with him to make, since he himself is a living proof of free-will, for Providence can never be supposed to have pre-ordained such a creature!

You go, Chesterfield!