I can't vouch for the veracity of all of these: you should double-check any you want to use.
I am well aware that I have not written anything but fictions… which is not to say they have nothing to do with the truth. - Michel Foucault
Truth is the only merit that gives dignity and worth to history. - Lord Acton (English historian)
The historian must not try to know what is truth, if he values his honesty: for if he cares for his truths, he is certain to falsify his facts. - Henry Adams
... historians ought to be precise, truthful, and quite unprejudiced, and neither interest nor fear, hatred nor affection, should cause them to swerve from a path of truth, whose mother is history. - Miguel de Cervantes (Don Quixote)
History is the witness of the times, the light of truth, the life of memory, the teacher of life, the messenger of antiquity. - Cicero
Poetry is nearer to vital truth than history. - Plato
If an historian were to relate truthfully all the crimes, weaknesses and disorders of mankind, his readers would take his work for satire rather than for history. -Pierre Bayle, Historical and Critical Dictionary
It is a great pity that every human being does not, at an early stage of his life, have to write a historical work. He would then realize that the human race is in quite a jam about truth. - Rebecca West
Whosoever, in writing a modern history, shall follow truth too near the heels, it may haply strike out his teeth. - Walter Raleigh, History of the World
History warns us... that it is the customary fate of new truths to begin as heresies and to end as superstitions. - Thomas Henry Huxley
To know the truth of history is to realize its ultimate myth and its inevitable ambiguity. - Roy P. Basler
Who does not know that the first law of historical writing is the truth. - Cicero
I don't believe the truth will ever be known, and I have a great contempt for history. - Gen. George Meade
Everyone falsifies history even if it is only his own personal history. Sometimes the falsification is deliberate, sometimes unconscious; put always the past is altered to suit the needs of the present. The best we can say of any account is not that it is the real truth at last, but that this is how the story appears now. - Joseph Freeman
The first law of history is to dread uttering a falsehood; the next is not to fear stating the truth; lastly, the historian's writings should be open to no suspicion of partiality or animosity. - Leo XIII
History is not history unless it is the truth. - Abraham Lincoln
Historian, discover the truth and publish it. - Inscription over the grave of Oklahoma historian Angie Debo.
[History is] an accumulative science, gradually gathering truth through the steady and plodding efforts of countless practitioners turning out countless monographs. - Gordon Wood
We have lost our grip on historical truth. - Joyce Appleby, Lynn Hunt, and Margaret Jacob in Telling the Truth About History
History, facts and truth are all Divine Products, and must prevail. - Charles A. Briggs
It takes three facts to make a truth. - Eugene Manlove Rhodes [Now there's a name!]
As the primary end of History is to record truth, impartiality, fidelity and accuracy are the fundamental qualities of an Historian. - Hugh Blair
A history in which every particular incident may be true may on the whole be false. - Thomas Babington Macaulay
These next few don't use the word 'truth' but are sorta kinda somewhat still on that topic:
History: An account mostly false, of events unimportant, which are brought about by rulers mostly knaves, and soldiers mostly fools. - Ambrose Bierce (US writer)
History is just one long string of atrocities. You could say history is atrocious. The best way to find out what they did is to find out where they hid the bodies. - David Bradley (The Chaneysville Incident, 1981)
Such a lot of things seem to me such rot. History, for example. Why it's quite different out of different books. - Agatha Christie (The Moving Finger)
All history is contemporary history. - Benedetto Croce (1941) [one of my favourites]
History is more or less bunk. - Henry Ford (Chicago Tribune, May 25, 1916)
History is not a narrative of events. The historian's difficult task is to explain what happened. - Christopher Hill (English historian)
The essential matter of history is not what happened but what people thought or said about it. - F.W. Maitland (English historian)
All the ancient histories, as one of our wits say, are just fables that have been agreed upon. - Voltaire, Jeannot et Colin
God cannot alter the past, though historians can. - Samuel Butler, "Prose Observations"
Historian: an unsuccessful novelist. - H.L. Mencken
Most history is guessing, and the rest is prejudice. - Will and Ariel Durant, Our Oriental Heritage
History is a pack of lies about events that never happened told by people who weren't there. - George Santayana [not at all sure about this ascription]
"The past is a place of fantasy." - Hayden White
It is not the literal past, the 'facts' of history, that shape us, but images of the past embodied in language." - Brian Friel
History is a science, no more and no less. - J. B. Bury
Nothing falsifies history more than logic. - Guizot
[History is] not factual at all, but a series of accepted judgments. - Geoffrey Barraclough
History, to be above evasion or dispute, must stand on documents, not on opinions. - Lord Acton
Let the science and research of the historian find the fact and let his imagination and art make clear its significance. - George Trevelyan
The past has always been the handmaid of authority. - J.H. Plumb
History is not a catalogue but…a convincing version of events. - A.J.P. Taylor
History is the great propagator of doubt. - A.J.P. Taylor
History is often not what actually happened but what is recorded as such. - Henry L. Stimson
There is no history, only histories. - Karl Popper