Also attributed to Alexander Fraser Tytler (1747-1813)... who knows... in any event, the quote has been around since the 1950s and is still very true.
Neal Boortz used to have this quote on his website years ago. He also said not to believe anything unless you personally verified it. I checked with the National Museum of Scotland and exchanged emails with the custodian of the Tytler collected works. He said it sounded more like a 20th century rant.
If you do a search for this quote the only place you will ever find it is on Conservative websites and blogs, never a link to a genuine passage from any speech or book by any author anywhere. It's bogus.