“Military intelligence was as nothing to military stupidity.”

In Memory Yet Green (1979), p. 461
General sources

Kissinger has denied saying it.
The only evidence that Kissinger ever said this was a claim in the book, The Final Days, by Bob Woodward and Carl Bernstein, in chapter 14 (p.194 in the 1995 paperback edition). Woodward & Bernstein claimed that one of Kissinger's political foes, Alexander Haig, had told someone unnamed, that he (Haig) had heard Kissinger say it. That's triple hearsay, made even weaker by the fact that one of the parties is anonymous. Kissinger has denied ever saying it, and it was never substantiated by Haig, nor by anyone of known identity who claimed to have heard it. As Kirkus Reviews noted about the whole book, "none of it is substantiated in any assessable way."
In fact, the quote is not even very plausible, on its face. Kissinger served with distinction in the U.S. Army during WWII, and was awarded the Bronze Star. He has always been very respectful of other servicemen and their sacrifices. For him to have said such a thing would have been wildly out of character. In fact, the awkward phrasing doesn't even sound like Kissinger, whose English prose is consistently measured and careful, despite his heavy accent, even when he speaks extemporaneously.
Misattributed

Source: Friday (1982), Chapter 4 (p. 37)

Ch XVI : The Great Retreat, p. 347.
The Rommel Papers (1953)

Woodward and Bernstein. The Final Days, chapter 14 (1976)

Hometown Annapolis - County Executive Leopold's FY08 Budget Address http://www.hometownannapolis.com/cgi-bin/read/2007/05_02-02/TOP

Source: The Guns of August

Quoted in Wilford, H: The New York Intellectuals: From Vanguard to Institution, Manchester University Press, 1995.
1990s

Inaugural Address (4 March 1845).