“That’s no malarkey, That's a fact.”

Source: Time Tunnel (1964), Chapter 9 (p. 140).

2
Original German: Was der Fall ist, die Tatsache, ist das Bestehen von Sachverhalten.
1920s, Tractatus Logico-Philosophicus (1922)

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

Quantum explanations http://lesswrong.com/lw/pc/quantum_explanations/ (April 2008), part of his Quantum Physics Sequence http://lesswrong.com/lw/r5/the_quantum_physics_sequence/.
Context: There are no surprising facts, only models that are surprised by facts; and if a model is surprised by the facts, it is no credit to that model.

Notes Toward a Supreme Fiction (1942), It Must Give Pleasure
Variant: Beyond which thought could not progress as thought.
Context: The nothingness was a nakedness, a point,Beyond which fact could not progress as fact.
Thereon the learning of the man conceived
Once more night’s pale illuminations, goldBeneath, far underneath, the surface of
His eye and audible in the mountain of
His ear, the very material of his mind.</p

Source: Small Great Things

Gottlob Frege (1956). "The thought: A logical inquiry" in: Peter Ludlow (1997) Readings in the Philosophy of Language. p. 27

Source: 1830s, Nature http://www.emersoncentral.com/nature.htm (1836), Ch. 4, Language