“A fact never went into partnership with a miracle. Truth does not need the assistance of miracle. A fact will fit every other fact in the Universe, because it is the product of all other facts. A lie will fit nothing except another lie made for the express purpose of fitting it.”

The Time of the Hero (1963)

The earliest published attribution of this quote to Einstein found on Google Books is the 1991 book The Art of Computer Systems Performance Analysis by Raj Jain (p. 507), but no source to Einstein's original writings is given and the quote itself is older; for example New Guard: Volume 5, Issue 3 from 1961 says on p. 312 http://books.google.com/books?id=5BbZAAAAMAAJ&q=%22fit+the+theory%22#search_anchor "Someone once said that if the facts do not fit the theory, then the facts must be changed", while Product engineering: Volume 29, Issues 9-12 from 1958 gives the slight variant on p. 9 "There is an age-old adage, 'If the facts don't fit the theory, change the theory.' But too often it's easier to keep the theory and change the facts." These quotes are themselves probably variants of an even earlier saying which used the phrasing "so much the worse for the facts", many examples of which can be seen in this search http://www.google.com/search?tbo=p&tbm=bks&q=facts+fit+%22so+much+the+worse+for+the+facts%22&tbs=,cdr:1,cd_max:Dec%2031_2%201950&num=10; for example, the 1851 American Whig Review, Volumes 13-14 says on p. 488 http://books.google.com/books?id=910CAAAAIAAJ&pg=PA488#v=onepage&q&f=false "However, Mr. Newhall may possibly have been of that casuist's opinion, who, when told that the facts of the matter did not bear out his hypothesis, said 'So much the worse for the facts.'" The German idealist philosopher Johann Gottlieb Fichte circa 1800 did say "If theory conflicts with the facts, so much the worse for the facts." The Hungarian Marxist Georg Lukacs in his "Tactics and Ethics" (1923) echoed the same quotation.
Misattributed

Source: The Golden Bough (1890), Chapter 5, The Magical Control of the Weather.

Eula Varner Snopes to Gavin Stevens in Ch. 20
The Town (1957)

Source: Sword of Destiny

Gavin Stevens to V. K. Ratliff in Ch. 24
The Town (1957)

E. Jephcott, trans., p. 9.
Dialektik der Aufklärung [Dialectic of Enlightenment] (1944)

E. Jephcott, trans., p. 9
Dialektik der Aufklärung [Dialectic of Enlightenment] (1944)

Anathemas and Admirations (1987)