If A. can prove, however conclusively, that he may, of right, enslave B. — why may not B. snatch the same argument, and prove equally, that he may enslave A?
You say A. is white, and B. is black. It is color, then; the lighter having the right to enslave the darker? Take care. By this rule, you are to be slave to the first man you meet, with a fairer skin than your own.
You do not mean color exactly? — You mean the whites are intellectually the superior of blacks, and, therefore, have the right to enslave them? Take care again. By this rule, you are to be slave to the first man you meet, with an intellect superior to your own.
But, say you, it is a question of interest; and, if you can make it your interest, you have the right to enslave another. Very well. And if he can make it his interest, he has the right to enslave you.

Abraham Lincoln (1809-1865) American lawyer, politician, US President (1861-65)

Note (1854-07-01?), On Slavery (fragment)
    (Source)

The note itself is not dated. The fragment is included in The Collected Works of Abraham Lincoln, Vol. 2 (1953) [ed. Roy P. Basler]. The printed version of the book gives "July 1, 1854?" as the date, as being the date assigned by Nicolay and Hay; the U. of Michigan online version of that work gives "April 1, 1854?" with no explaination. The editors of the Collected Works do note that it likely was written 1858-1859. The Abraham Lincoln Digital Library version suggests the note post-dates the Kansas-Nebraska Act (May 1854), which brought Lincoln back into politics, campaigning for a Whig congressional candidate in the Fall of 1854.