“We renounce all your spectacles, as strongly as we renounce the matters originating them, which we know were conceived of superstition, when we give up the very things which are the basis of their representations. Among us nothing is ever said, or seen, or heard, which has anything in common with the madness of the circus, the immodesty of the theatre, the atrocities of the arena, the useless exercises of the wrestling-ground.”

Letter to Thomas Jefferson (17 January 1820). Often misquoted as "God is an essence that we know nothing of" and attached to a part of his 22 January 1825 letter to Thomas Jefferson.
1820s

Part I : Ambiguity and Freedom
The Ethics of Ambiguity (1947)
Context: The failure described in Being and Nothingness is definitive, but it is also ambiguous. Man, Sartre tells us, is “a being who makes himself a lack of being in order that there might be being.” That means, first of all, that his passion is not inflicted upon him from without. He chooses it. It is his very being and, as such, does not imply the idea of unhappiness. If this choice is considered as useless, it is because there exists no absolute value before the passion of man, outside of it, in relation to which one might distinguish the useless from the useful. The word “useful” has not yet received a meaning on the level of description where Being and Nothingness is situated. It can be defined only in the human world established by man’s projects and the ends he sets up. In the original helplessness from which man surges up, nothing is useful, nothing is useless. It must therefore be understood that the passion to which man has acquiesced finds no external justification. No outside appeal, no objective necessity permits of its being called useful. It has no reason to will itself. But this does not mean that it can not justify itself, that it can not give itself reasons for being that it does not have. And indeed Sartre tells us that man makes himself this lack of being in order that there might be being. The term in order that clearly indicates an intentionality. It is not in vain that man nullifies being. Thanks to him, being is disclosed and he desires this disclosure. There is an original type of attachment to being which is not the relationship “wanting to be” but rather “wanting to disclose being.” Now, here there is not failure, but rather success.

On Truth and Lie in an Extra-Moral Sense (1873)

as quoted in Letters of the great artists – from Ghiberti to Gainsborough, Richard Friedenthal, Thames and Hudson, London, 1963, p . 232
1908 - 1920, On Mystery and Creation, Paris 1913

An Interview by Sheena McDonald (1995)

"Down the River", p. 147
Desert Solitaire (1968)

XI, 26, Parts of this passage has been heavily compared with later statements of René Descartes; in Latin and with a variant translations:
The City of God (early 400s)
Context: We both are, and know that we are, and delight in our being, and our knowledge of it. Moreover, in these three things no true-seeming illusion disturbs us; for we do not come into contact with these by some bodily sense, as we perceive the things outside of us of all which sensible objects it is the images resembling them, but not themselves which we perceive in the mind and hold in the memory, and which excite us to desire the objects. But, without any delusive representation of images or phantasms, I am most certain that I am, and that I know and delight in this. In respect of these truths, I am not at all afraid of the arguments of the Academicians, who say, What if you are deceived? For if I am deceived, I am. For he who is not, cannot be deceived; and if I am deceived, by this same token I am. And since I am if I am deceived, how am I deceived in believing that I am? for it is certain that I am if I am deceived. Since, therefore, I, the person deceived, should be, even if I were deceived, certainly I am not deceived in this knowledge that I am. And, consequently, neither am I deceived in knowing that I know. For, as I know that I am, so I know this also, that I know. And when I love these two things, I add to them a certain third thing, namely, my love, which is of equal moment. For neither am I deceived in this, that I love, since in those things which I love I am not deceived; though even if these were false, it would still be true that I loved false things. For how could I justly be blamed and prohibited from loving false things, if it were false that I loved them? But, since they are true and real, who doubts that when they are loved, the love of them is itself true and real? Further, as there is no one who does not wish to be happy, so there is no one who does not wish [themself] to be [into being]. For how can he be happy, if he is nothing?

§ 118
Philosophical Investigations (1953)

Essay on the Theory of Painting (1725)