“Agnosticism is not properly described as a "negative" creed, nor indeed as a creed of any kind, except in so far as it expresses absolute faith in the validity of a principle which is as much ethical as intellectual. This principle may be stated in various ways, but they all amount to this: that it is wrong for a man to say that he is certain of the objective truth of any proposition unless he can produce evidence which logically justifies that certainty.”

Principles of Mathematics (1903), Ch. I: Definition of Pure Mathematics, p. 3
1900s

Concerning the Jews (Harper's Magazine, Sept. 1899)
Variant: I have no race prejudices nor caste prejudices nor creed prejudices. All I care to know is that a man is a human being, and that is enough for me; he can't be any worse.

Ideology and Utopia (1929)

1910s, Address to the Knights of Columbus (1915)
Context: Our nation was founded to perpetuate democratic principles. These principles are that each man is to be treated on his worth as a man without regard to the land from which his forefathers came and without regard to the creed which he professes. If the United States proves false to these principles of civil and religious liberty, it will have inflicted the greatest blow on the system of free popular government that has ever been inflicted. Here we have had a virgin continent on which to try the experiment of making out of divers race stocks a new nation and of treating all the citizens of that nation in such a fashion as to preserve them equality of opportunity in industrial, civil, and political life. Our duty is to secure each man against any injustice by his fellows.

No. 185 http://archive.twoaspirinsandacomedy.com/spectator/spectator.php?line=185 (2 October 1711).
Often misquoted as "To be an atheist requires an infinitely greater measure of faith than to receive all the great truths which atheism would deny."
The Spectator (1711–1714)

1910s, Address to the Knights of Columbus (1915)
Context: One of the most important things to secure for him is the right to hold and to express the religious views that best meet his own soul needs. Any political movement directed against anybody of our fellow- citizens because of their religious creed is a grave offense against American principles and American institutions. It is a wicked thing either to support or to oppose a man because of the creed he professes. This applies to Jew and Gentile, to Catholic and Protestant, and to the man who would be regarded as unorthodox by all of them alike. Political movements directed against men because of their religious belief, and intended to prevent men of that creed from holding office, have never accomplished anything but harm. This was true in the days of the ‘Know-Nothing’ and Native-American parties in the middle of the last century; and it is just as true to-day. Such a movement directly contravenes the spirit of the Constitution itself. Washington and his associates believed that it was essential to the existence of this Republic that there should never be any union of Church and State; and such union is partially accomplished wherever a given creed is aided by the State or when any public servant is elected or defeated because of his creed. The Constitution explicitly forbids the requiring of any religious test as a qualification for holding office. To impose such a test by popular vote is as bad as to impose it by law. To vote either for or against a man because of his creed is to impose upon him a religious test and is a clear violation of the spirit of the Constitution.

Source: Carnap’s intellectual biography (1963), p. 62

Theorem II
Monas Hieroglyphica (1564)

Source: A logical calculus of the ideas immanent in nervous activity (1943), p. 115