“There is nothing so absurd that it has not been said by some philosopher.”

Nullum est iam dictum quod non dictum sit prius.
Prologue, Line 41.
Variant translation: Nothing has yet been said that’s not been said before.
Eunuchus

Part 4, Section 7
A Treatise of Human Nature (1739-40), Book 1: Of the understanding
Context: This deficiency in our ideas is not, indeed, perceived in common life, nor are we sensible, that in the most usual conjunctions of cause and effect we are as ignorant of the ultimate principle, which binds them together, as in the most unusual and extraordinary. But this proceeds merely from an illusion of the imagination; and the question is, how far we ought to yield to these illusions. This question is very difficult, and reduces us to a very dangerous dilemma, whichever way we answer it. For if we assent to every trivial suggestion of the fancy; beside that these suggestions are often contrary to each other; they lead us into such errors, absurdities, and obscurities, that we must at last become asham'd of our credulity. Nothing is more dangerous to reason than the flights of the imagination, and nothing has been the occasion of more mistakes among philosophers. Men of bright fancies may in this respect be compar'd to those angels, whom the scripture represents as covering their eyes with their wings. This has already appear'd in so many instances, that we may spare ourselves the trouble of enlarging upon it any farther.

Natural Theology (1836), Bk. II, Ch. III : On the Strength of the Evidences for a God in the Phenomena of Visible and External Nature, § 15; though provided without attribution of author, the saying "There is nothing more uncommon than common sense" has since become misattributed to particular people, including Frank Lloyd Wright.

Source: Sanitary Economy (1850), p. 28-29
Context: It has been among the visions of some dreaming philosophers that human life is capable of almost indefinite extension. The great Condorcet was one of these. He thought that by the removal of the two causes of evil—poverty and superfluity—by destroying prejudices and superstitions, and by various other operations, which he considered the purification of mankind, but which other people would call their pollution, the approach of death would by degrees be farther and farther indefinitely protracted. It is desirable that the practical views entertained by sanitary reformers should be kept widely distinct from any such theories, the character of which has been well drawn by Malthus when he says—"... Though I may not be able in the present instance to mark the limit at which further improvement will stop I can very easily mention a point at which it will not arrive."

Source: The Problems of Philosophy

True though this may have been in the past, it is true no longer. The science of our century has forged weapons of observation and analysis by which the veriest tyro may profit. Science has trained and fashioned the average mind into habits of exactitude and disciplined perception, and in so doing has fortified itself for tasks higher, wider, and incomparably more wonderful than even the wisest among our ancestors imagined. Like the souls in Plato's myth that follow the chariot of Zeus, it has ascended to a point of vision far above the earth. It is henceforth open to science to transcend all we now think we know of matter and to gain new glimpses of a profounder scheme of Cosmic law.
Address to the British Association for the Advancement of Science (1898)

Sigmund Freud, in a letter to Siegfried Hessing. As quoted in António Damásio's Looking for Spinoza: Joy, Sorrow, and the Feeling Brain (Orlando, FL: Harcourt, 2003)
A - F

Un philosophe digne de ce nom n'a jamais dit qu'une seule chose : encore a-t-il plutôt cherché à la dire qu'il ne l'a dite véritablement. Et il n'a dit qu'une seule chose parce qu'il n'a su qu'un seul point : encore fut-ce moins une vision qu'un contact...
"L’intuition philosophique (Philosophical Intuition)" http://obvil.paris-sorbonne.fr/corpus/critique/bergson_pensee/body-5 (10 April 1911); translated by Mabelle L. Andison in: Henri Bergson, The Creative Mind: An Introduction to Metaphysics, Courier Dover Publications, 2012, p. 91