“These eight rules [above] contain all the precepts for solid and immutable proofs.”

Preface.
A Treatise on Language: Or, The Relation which Words Bear to Things, in Four Parts (1836)
Context: All that the book contains is the elucidation of but one precept: namely, to interpret language by nature. We [generally and incorrectly] reverse the rule and interpret nature by language.

(1945)

Source: Resurrection: Myth or Reality? (1994), p. 37

Source: The Rise & Fall of Society (1959), p. 77

Note written on the margins of his copy of Claude-Gaspar Bachet's translation of the famous Arithmetica of Diophantus, this was taken as an indication of what became known as Fermat's last theorem, a correct proof for which would be found only 357 years later; as quoted in Number Theory in Science and Communication (1997) by Manfred Robert Schroeder

How to Write History

Source: The Tenant of Wildfell Hall (1848), Ch. XX : Persistence; Mr. Maxwell to Helen

Hélas! les vices de l’homme, si pleins d’horreur qu’on les suppose, contiennent la preuve (quand ce ne serait que leur infinie expansion!) de son goût de l’infini.
"Le poème du haschisch," I: Le goût de l’infini http://fr.wikisource.org/wiki/Les_Paradis_artificiels_-_I
Les paradis artificiels (1860)

al'Lan Mandragoran
(15 November 1990)
Source: The Great Hunt