The phrase’s earliest printed reference is in John Harington’s 1657 poem The History of Polindor and Flostella. The poem sends a clear message, that decent people stay inside the pale.
The poem was published quite a bit after Harington’s death. He also wrote ‘A Short View of the State of Ireland’, having served there with Essex, so I think it’s clear which Pale he was referring to.
I’m not sure if or where the specific phrase ‘beyond the Pale’ was used earlier than that.