“To give an accurate and exhaustive account of that period would need a far less brilliant pen than mine.”

Part 1.3 Rights of Man
1790s, Rights of Man, Part I (1791)

Le forze della penna sono troppo maggiori che coloro non estimano che quelle con conoscimento provato non hanno.
Eighth Day, Seventh Story
The Decameron (c. 1350)

Fragment ix.
Golden Sayings of Epictetus, Fragments

100 Years of Mathematics: a Personal Viewpoint (1981)

The earliest published source located on Google Books attributing this to Einstein is the 2000 book The Internet Handbook for Writers, Researchers, and Journalists by Mary McGuire, p. 14 http://books.google.com/books?id=Sb-v0K2EkNAC&q=einstein#search_anchor. It was attributed to him on the internet before that, as in this post from 1997 http://groups.google.com/group/comp.graphics.apps.lightwave/msg/d13c55cc4cca4867?hl=en. Variants of the quote can be found well before this however, as in the 1989 book Urban Surface Water Management by S. G. Walesh, which on p. 315 http://books.google.com/books?id=-LcZUPtDykQC&q=%22beyond+imagination%22#v=snippet&q=%22beyond%20imagination%22&f=false contains the statement (said to have been 'stated anonymously'): "The computer is incredibly fast, accurate, and stupid. Man is unbelievably slow, inaccurate, and brilliant. The marriage of the two is a challenge and opportunity beyond imagination." Even earlier, the article "A Paper Industry Application of Systems Engineering and Direct Digital Control" http://books.google.com/books?id=A-YpAQAAIAAJ&q=%22and+direct+digital+control%22#search_anchor by H. D. Couture, Jr. and M. A. Keyes, which appears in the 1969 Advances in Instrumentation: Vol. 24, Part 4, has a statement on this page http://books.google.com/books?id=A-YpAQAAIAAJ&q=%22Computers+are+incredibly+fast%2C+accurate+and+stupid%22#search_anchor which uses phrasing similar to the supposed Einstein quote in describing computers and people: "Computers are incredibly fast, accurate, and stupid. On the other hand, a well trained operator as compared with a computer is incredibly slow, inaccurate and brilliant." Variants with slightly different wording can be found earlier than 1969, as in this April 1968 article http://journals.lww.com/joem/Citation/1968/04000/Fast,_Accurate_and_Stupid.10.aspx. The earliest source located, and most likely the origin of this saying, is an article titled "Problems, Too, Have Problems" by John Pfeiffer, which appeared in the October 1961 issue of Fortune magazine. As quoted here http://books.google.com/books?id=TwwQAAAAIAAJ&q=%22Man+is+a+slow%2C+sloppy%2C+and+brilliant+thinker%3B+computers+are+fast%2C+accurate%2C+and+stupid%22#search_anchor, Pfeiffer's article contained the line "Man is a slow, sloppy, and brilliant thinker; computers are fast, accurate, and stupid."
Misattributed

Source: Aphorisms and Reflections (1901), p. 148

Chpt.3, p. 35
Principles of Geology (1832), Vol. 1
Context: Dr. Plot, in his 'Natural History of Oxfordshire.' (1677) attributed to a 'plastic virtue latent in the earth' the origin of fossil shells and fishes; and Lister, to his accurate account of British shells, in 1678, added the fossil species, under the appellation of turbinated and bivalve stones. 'Either,' said he, 'these were terriginous, or if otherwise, the animals they so exactly represent have become extinct. This writer appears to have been the first who was aware of the continuity over large districts of the principal groups of strata in the British series, and who proposed the construction of regular geological maps.

"The Expanding Mental Universe", Saturday Evening Post (July 1959)
1950s