Ohio

The author of the OP was none other than George Washington's Step-Grandson,
George Washington Parke Custis. To borrow terminology from epidemiology, he
is the Index Case for this legend. In his Recollections of George Washington
(published 1857) the OP is written just about word for word. In a footnote to
the story, Custis says that he was told the story after Washington's death by
Dr. Craik, a long-time friend of GW's, who was at the battle, accompanied
Washington to Ohio in 1772 or so and would have been at the alleged meeting,
and may have inadvertently killed Washington by bleeding him during an illness.

Thankfully, the BPGW author cites that work. Unfortunately, he doesn't cite
an earlier work, also by Custis, published about 30 years earlier...a play
called "The Indian Prophecy". By modern standards this is a remarkably
mediocre play. The lines in the OP are the final words of the play, delivered
by the fictional Menawa just before the curtain comes down. In fact, as far
as I can tell, the entire play exists simply to allow this Indian to deliver
his lines. In the era that the play was put on, it probably went over incredibly well, though.

For those friendly non-Americans (and some Americans) that peruse these boards, Washington was a man who became quite literally a legend in his own time and in the 19th through the better part of the 20th Century, Washington had a heroic quality that would amaze many today. In the era that The Indian Prophecy played, it would have been very well received…doubly so as it was written by a member of that august family.

So the question becomes...how much do you trust Mr. Custis? Neither
Washington nor Craik have left us a shred of evidence that the meeting took
place. The former's journals account for the trip to the Ohio circa 1770, but
include no mention of any such prophecy. The latter apparently left no known
diary (or at least none I can find) and the good doctor died over 10 years
before the play was published. This means that Mr. Custis has about zero
corroboration and, to make things worse, he had a lot of good reasons to
"fluff-up" the legend.

Custis was the de factor heir to the Washington legend. In the early 19th
Century the Washington legend was rampant and patriotism was very much in
vogue. He had strong ties to his step-grandfather and at least one reference
I read referred to his "obsession" with Washington. Add to that that Mr.
Custis could & did make money by presenting legends of Washington, and one
can't help wondering about the validity of the legend.

Despite being a staple in American text-books from about 1860 to the early
1930s (along with stories of chopping down cheery trees and throwing coins
across rivers), the lack of a paper trail doesn't hold water for this legend.
Did it happen? Maybe....but the lack of contemporary accounts makes it very
suspect. I'd have to give this one a thumbs down.