“From a persuasion that equal liberty was originally the Portion, It is still the Birthright of all men.”

An essay on the slavery and commerce of the human species, particularly the African, translated from a Latin Dissertation, p. 54 (1788) https://books.google.com/books?id=pBOe7105MhMC&pg=PA54

Inscription on monument

12th Annual Report to the Massachusetts State Board of Education http://www.tncrimlaw.com/civil_bible/horace_mann.htm (1848); published in Life and Works of Horace Mann Vol. III, (1868) edited by Mary Mann, p. 669
Context: Education, then, beyond all other devices of human origin, is the great equalizer of the conditions of men, — the balance-wheel of the social machinery. I do not here mean that it so elevates the moral nature as to make men disdain and abhor the oppression of their fellow-men. This idea pertains to another of its attributes. But I mean that it gives each man the independence and the means by which he can resist the selfishness of other men. It does better than to disarm the poor of their hostility towards the rich: it prevents being poor.

Source: The Anarchist Cookbook (1971), Chapter Three: "Natural, Nonlethal, and Lethal Weapons", p. 93.

This they said, and this meant. They did not mean to assert the obvious untruth, that all were then actually enjoying that equality, nor yet, that they were about to confer it immediately upon them. In fact they had no power to confer such a boon. They meant simply to declare the right, so that the enforcement of it might follow as fast as circumstances should permit. They meant to set up a standard maxim for free society, which should be familiar to all, and revered by all; constantly looked to, constantly labored for, and even though never perfectly attained, constantly approximated, and thereby constantly spreading and deepening its influence, and augmenting the happiness and value of life to all people of all colors everywhere. The assertion that "all men are created equal" was of no practical use in effecting our separation from Great Britain; and it was placed in the Declaration, nor for that, but for future use. Its authors meant it to be, thank God, it is now proving itself, a stumbling block to those who in after times might seek to turn a free people back into the hateful paths of despotism. They knew the proneness of prosperity to breed tyrants, and they meant when such should re-appear in this fair land and commence their vocation they should find left for them at least one hard nut to crack. I have now briefly expressed my view of the meaning and objects of that part of the Declaration of Independence which declares that "all men are created equal".
1850s, Speech on the Dred Scott Decision (1857)

Speech in reply to Senator Stephen Douglas in the Lincoln-Douglas debates http://www.bartleby.com/251/1003.html of the 1858 campaign for the U.S. Senate, at Chicago, Illinois (10 July 1858)
1850s, Lincoln–Douglas debates (1858)
Context: My friend has said to me that I am a poor hand to quote Scripture. I will try it again, however. It is said in one of the admonitions of our Lord, "As your Father in Heaven is perfect, be ye also perfect." The Saviour, I suppose, did not expect that any human creature could be perfect as the Father in Heaven; but He said, "As your Father in Heaven is perfect, be ye also perfect." He set that up as a standard; and he who did most toward reaching that standard, attained the highest degree of moral perfection. So I say in relation to the principle that all men are created equal, let it be as nearly reached as we can. If we cannot give freedom to every creature, let us do nothing that will impose slavery upon any other creature. Let us then turn this Government back into the channel in which the framers of the Constitution originally placed it. Let us stand firmly by each other. If we do not do so we are turning in the contrary direction, that our friend Judge Douglas proposes — not intentionally — as working in the traces tend to make this one universal slave nation. He is one that runs in that direction, and as such I resist him. My friends, I have detained you about as long as I desired to do, and I have only to say, let us discard all this quibbling about this man and the other man; this race and that race and the other race being inferior, and therefore they must be placed in an inferior position; discarding our standard that we have left us. Let us discard all these things, and unite as one people throughout this land, until we shall once more stand up declaring that all men are created equal. My friends, I could not, without launching off upon some new topic, which would detain you too long, continue to-night. I thank you for this most extensive audience that you have furnished me to-night. I leave you, hoping that the lamp of liberty will burn in your bosoms until there shall no longer be a doubt that all men are created free and equal.

Aristotle, Politics, Book V 1301a.29-31
Politics

Those are undeniable truths.
Vietnamese Proclamation of Independence (2 September 1945), Ho Chi Minh, Selected Works (1960-1962), Vol. 3, pp. 17-21