I remember this variation of the story:

An unknown chessplayer bet a lot of money, that he could play live & simultaniously against two grandmasters and achieve at least 1 point. The two matches were played in different rooms next to each other. No one except the unknown player was allowed to switch rooms during the matches (to not disturb the grandmasters). Obviously he played White against one grandmaster, Black against the other, and won his bet.

As I sometimes tell this anecdote, I wonder what its actual source might be?

I'm pretty confident, this never happend in real, as I expect no grandmaster could get scammed that easily. But the story could be rooted in a "catch me if you can"-like movie or novel or something.

If someone knows more, I would be happy for a hint...