Looking for Baal Shem Tov - Story

B"H

Maybe someone here can help me finding a certain story from the Baal Shem Tov. I read this story many years ago on the Internet. Probably on a Chabad or Breslov site. I do not know the name of the story and only a few details.

Basically the story is about the Baal Shem Tov sending someone to a certain place and on his way he comes to an island or village. There the man helps the king who, in return, promises him that all the Jews can come to live in his village / island. The man goes back to the Baal Shem Tov who refuses to move there due to missing sparks.

I am looking for the exact name and context of the story.

Miriam