This reads so much like an urban legend, that I had to poke around a bit. It appears that it was a piece of fiction written by a Williston Fisk for Harper's Weekly in 1898, and has been given various backstories as time went on.

For those who want a reference: https://archive.org/details/sim_harpers-weekly_1898-09-03_42...

Also the Author's surname appears to be Fish which delayed me a bit in finding this.

See also e.g. https://tarlton.law.utexas.edu/last-will-of-williston-fish