Sherman: "Well, Grant, we've had the devil's own day, haven't we?"
Grant: "Yes. Lick 'em tomorrow though."
I recently tried to trace the original source of the quote and came to the conclusion that it is a later invention. This soundbite enters ACW historiography in 1960, in Bruce Catton's "Grant Moves South". It is not present in any previous history, nor in either Grant nor Sherman's memoirs.
Thanks to the large scale digitisation of millions of books we can do keyword searches. I've found the phrase only once before 1960, in Charles Wingate's "What Shall Our Boys Do For a Living":
We can assume this is the ultimate source of the soundbite, and we have to assume as Catton was not big on citations. The Napoleon quote also doesn't seem to appear until around the time of the Civil War (when it appears in American magazines).
Thus it appears that the phrase was invented by Wingate ca. 1898, used without citation or verification by Catton in 1960 and has been promulgated unquestioned ever since.