“It is incredible that only idiots are absolutely sure of salvation. It is incredible that the more brain you have the less your chance is. There can be no danger in honest thought, and if the world ever advances beyond what it is to-day, it must be led by men who express their real opinions.”

Source: Love Is a Dog from Hell

The trial of Charles B. Reynolds for blasphemy (1887)
Context: The question to be tried by you is whether a man has the right to express his honest thought; and for that reason there can be no case of greater importance submitted to a jury. And it may be well enough for me, at the outset, to admit that there could be no case in which I could take a greater — a deeper interest. For my part, I would not wish to live in a world where I could not express my honest opinions. Men who deny to others the right of speech are not fit to live with honest men.
I deny the right of any man, of any number of men, of any church, of any State, to put a padlock on the lips — to make the tongue a convict. I passionately deny the right of the Herod of authority to kill the children of the brain.
A man has a right to work with his hands, to plow the earth, to sow the seed, and that man has a right to reap the harvest. If we have not that right, then all are slaves except those who take these rights from their fellow-men.

Responsible Scientific Investigation and Application (1976)

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

As quoted in

This Business of Living (1935-1950)

Girl, Interrupted (1994)

Speaking Of Love (1980)
Context: DON'T MISS LOVE. It's an incredible gift. I love to think that the day you're born, you're given the world as your birthday present. It frightens me to think that so few people even bother to open up the ribbon! Rip it open! Tear off the top! It's just full of love and magic and joy and wonder and pain and tears. All of the things that are your gift for being human.