I have a John Deer Sabre riding mower with a 13.5 HP Briggs and Straton engine. It stopped running. When I drained the oil it was filled with gasoline. What happened?

You have a possible intake valve sticking

I think you have a float problem in the carb and the needle and seat valve stuck open flooding the carb and shutting down the engine and gas into oil.

If you can list the No# here for the
Model #
Type#
Code#

I could hopefully find a manual and carb /engine brake down,