“This idea, though not incorporated in the constitution, was the prevailing idea at that time. The constitution, it is true, secured every essential guarantee to the institution while it should last, and hence no argument can be justly urged against the constitutional guarantees thus secured, because of the common sentiment of the day. Those ideas, however, were fundamentally wrong. They rested upon the assumption of the equality of races. This was an error.”

Source: Speech (June 1853), p. 79

Dissenting, DeFunis v. Odegaard, 416 U.S. 312 (1974)
Judicial opinions

The Notion of a Living Constitution https://web.archive.org/web/20071031034406/http://www.claremont.org/publications/precepts/id.169/precept_detail.asp.

Regarding using the words "slave" or "slavery" within the U.S. Constitution, in Madison's notes (25 August 1787)
Variants:
Madison, in convention, when an attempt was made to introduce the term slave into the Constitution, said: "It must not be so; because we intend this Constitution to be the great charter of human liberty to the unborn millions who shall enjoy its protection, and who should never see that such an institution as slavery has ever known in our midst."
As paraphrased or quoted in Our National Condition, and Its Remedy : A Sermon, Preached in the Pine Street Church, Boston, on Sunday, June 22, 1856 (1856) https://archive.org/details/ournationalcondi00dext by Henry Martyn Dexter
Madison said he "thought it wrong to admit in the Constitution the idea that there could be property in man. We intend this Constitution to be the great charter of human liberty to the unborn millions who may enjoy its protection, and who shall never see that such an institution was ever known in their midst.
As paraphrased or quoted in Reminiscences of James A. Hamilton: Or, Men and Events, at Home and Abroad (1869), Appendix D, Property in Man, p. 625 https://books.google.com/books?id=0uQEAAAAYAAJ&pg=PA625#v=twopage&q&f=false
1780s, The Debates in the Federal Convention (1787)
Context: Mr. MADISON thought it wrong to admit in the Constitution the idea that there could be property in men. The reason of duties did not hold, as slaves are not like merchandize, consumed, &c

Judge Napolitano on Hannity and Colmes http://www.youtube.com/watch?v=bejmEG_t9mI, discussing the Supreme Court rulings on the scope of the protections in the Constitution.
Context: The Constitution applies to persons, not just citizens. If you read the Constitution, its protections are not limited to Americans. And that was written intentionally, because at the time it was written, they didn't know what Native Americans would be. When the post civil war amendments were added, they didn't know how blacks would be considered, because they had a decision of the Supreme Court called Dred Scott, that said blacks are not persons. So in order to make sure the Constitution protected every human being: American, alien; citizen, non-citizen; lawful combatant, enemy combatant; innocent, guilty; those who wish us well, those who wish us ill... they use the broadest possible language, to make it clear: Wherever the government goes, the Constitution goes, and wherever the Constitution goes, the protections that it guarantees restrain the government and requires it to protect those rights.

As quoted in His Brother's Blood: Speeches and Writings, 1838–64 https://books.google.com/books?id=qMEv8DNXVbIC&pg=PA198 (2004), edited by William Frederick Moore and Jane Ann Moore, pp. 198–199
1860s, Speech to the U.S. House of Representatives (April 1860)

BBC World interview (2003)

2000s, The Central Idea (2006)
Context: According to Abraham Lincoln, public opinion always has a central idea from which all its minor thoughts radiate. The central idea of the American Founding—and indeed of constitutional government and the rule of law—was the equality of mankind. This thought is central to all of Lincoln's speeches and writings, from 1854 until his election as president in 1860. It is immortalized in the Gettysburg Address.

Fundamentals of Our Consitutions http://www.mormonnewsroom.org/article/fundamentals-of-our-constitutions-elder-dallin-h-oaks, 17 September 2010