On Oct. 3, 1789, George Washington signed a proclamation declaring Thanksgiving a national holiday.
Now one of the original copies of this single-sided piece of paper, which includes the founding father's signature—is about to hit the auction block at Christie's.
And with the potential to fetch $8 million to $12 million, the document could set a record, said Tom Lecky, Christie's Americas head of books and manuscripts.
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"It absolutely does stand to be the most expensive American manuscript documents ever sold at auction," he told CNBC.
"Washington signed very few proclamations. It's rare enough to have a proclamation at all, but to have a proclamation about a holiday that we all hold so dear, really deserves to be featured."