“I confess, Sir, I am at a loss to conceive how any man, who has ever read our Constitution as originally framed, or as it now exists, can listen a moment to such an argument. If anything be clearer than another on its face, it is, that it was intended to constitute a Christian State. I deny totally the gentleman's position, that the religious expressions it contains were intended only to show forth the pious sentiments of those who framed it. They were intended to incorporate into our system the principles of Christianity, — principles which belonged not only to those who framed, but to the whole people who adopted it. Sir, the people of that day were a Christian people; they adopted a Christian Constitution; they no more contemplated the existence of infidelity than the Athenian laws provided against the perpetration of parricide. They established a Christian Commonwealth; they wrote upon its walls, Salvation, and upon its gates, Praise; and Christianity is as clearly now its corner-stone, as if the initial letter of every page of our Statute Book, like that of some monkish manuscript, were illuminated with the figure of the Cross!”

Letter to his son http://radgeek.com/gt/2005/01/03/robert-e-Lee-owned-slaves-and-defended-slavery/, G. W. Custis Lee (23 January 1861).
1860s
Context: I can anticipate no greater calamity for the country than a dissolution of the Union. It would be an accumulation of all the evils we complain of, and I am willing to sacrifice everything but honor for its preservation. I hope, therefore, that all constitutional means will be exhausted before there is a resort to force. Secession is nothing but revolution. The framers of our Constitution never exhausted so much labor, wisdom, and forbearance in its formation, and surrounded it with so many guards and securities, if it was intended to be broken by every member of the Confederacy at will. It is intended for 'perpetual Union,' so expressed in the preamble, and for the establishment of a government, not a compact, which can only be dissolved by revolution, or the consent of all the people in convention assembled. It is idle to talk of secession: anarchy would have been established, and not a government, by Washington, Hamilton, Jefferson, Madison, and all the other patriots of the Revolution. … Still, a Union that can only be maintained by swords and bayonets, and in which strife and civil war are to take the place of brotherly love and kindness, has no charm for me. I shall mourn for my country and for the welfare and progress of mankind. If the Union is dissolved and the Government disrupted, I shall return to my native State and share the miseries of my people, and, save in defense will draw my sword on none.

Regarding using the words "slave" or "slaver" in the U.S. Constitution (25 August 1787); as quoted in "The Present Aspect of the Slavery Question" in Orations and Addresses of George William Curtis (1894), p. 69 https://books.google.com/books?id=y3RaAAAAMAAJ&pg=PA69&dq=%22We+intend+this+Constitution+to+be+the+great+charter+of+human+liberty+to+the+unborn+%22&hl=en&sa=X&ved=0CB0Q6AEwAGoVChMI2ai6jcCsxwIVRRs-Ch38_wz2#v=onepage&q=%22We%20intend%20this%20Constitution%20to%20be%20the%20great%20charter%20of%20human%20liberty%20to%20the%20unborn%20%22&f=false
1780s, The Debates in the Federal Convention (1787)

Source: 1980s, P. B. Medawar (1986), Memoir of a thinking radish: an autobiography, Oxford University Press, p. 117.

Part 1, Book 2, ch. 2, art. 1.
Philosophy of the Inductive Sciences (1840)

Townhall in Lancaster, Pennsylvania (31 March 2008) video https://www.youtube.com/watch?v=a3IWq3CXHyc
2008

U.S. Grant's "perfect speech" which he used on several occasions beginning in 1865, as quoted in Grant: A Biography (1982) by William S. McFeely, p. 234.
1860s
Context: I rise only to say that I do not intend to say anything. I thank you for your hearty welcomes and good cheers.

1850s, The Present Aspect of the Slavery Question (1859)

Page 14.
A Grammar of the English Language (1818)

2000s, Bush's Lincolnian Challenge (2002)