The early american presidents are infamous for being absolutely ruthless to each other in the press. Is there a particularly good source of evidence for these sorts of things or had any good monographs written about it?
Try https://founders.archives.gov. The site makes searchable the letters and other papers of the founding fathers. Plus, you can search the papers of a specific founding father. So, just click the link to search the papers of Thomas Jefferson, and from there, search from "washington" and you should find lots of different stuff that Jefferson wrote about Washington.
Beyond that, you'd probably want to also search historical newspapers of the era, though there's little in the way of direct quotes in newspaper articles in those days.