Who said I disapprove with what you say but I will defend to the death your right to say it?

This quote is regularly and, apparently, incorrectly attributed to either Voltaire or Patrick Henry. (See related links for sources.)

Though Voltaire merits some credit, the precise statement only occurs in the writing about Voltaire by Evelyn Beatrice Hall (pseudonym S. G. Tallentyre) in her biography of the master French author, satirist and philosopher, entitled "The Friends of Voltaire" (c. 1906).

The men who had hated [the book], and had not particularly loved Helvétius, flocked round him now. Voltaire forgave him all injuries, intentional or unintentional. 'What a fust about an omelette!' he had exlaimed when he heard of the burning. How abominably unjust to persecute a man for such an airy trifle as that! 'I disapprove of what you say, but I will defend to the death your right to say it,' was his attitude now.

Tallentyre herself does not attribute this quotation directly to Voltaire, but rather she uses it to summarize and/or generalize the thoughts of the author; thoughts expressed in a closely similar quotation which is indeed unique to Voltaire:

"Monsieur l'abbé, I detest what you write, but I would give my life to make it possible for you to continue to write," wrote Voltaire himself in a letter to Monsieur le Riche, dated February 6, 1770.

The congruous similarities between Tallentyre's rephrasing of ideas unique to Voltaire and Voltaire's own direct quotation of a nearly equivalent meaning justify the popular (albeit inaccurate) trend of most French, Francophone and/or Francophile peoples to attribute this quotation directly to Voltaire, just as Tallentyre most likely would have hoped.

Therefore, it is arguably neither completely correct nor completely incorrect to attribute this quote to Voltaire, when in fact the original source material was written by S. G. Tallentyre (a.k.a. Evelyn Beatrice Hall) in 1906 -- a century and a half after the death of Voltaire.

Related Links: An example of the misattribution of the quote is in the link to Dictionary and one of many correct references to the source is provided at Wikiquotes.