I always thought this was somewhat common knowledge. Here's a quote from Lincoln from the Lincoln-Douglas debates.
"I am not, nor ever have been, in favor of bringing about in any way the social and political equality of the white and black races, that I am not nor ever have been in favor of making voters or jurors of negroes, nor of qualifying them to hold office, nor to intermarry with white people; and I will say in addition to this that there is a physical difference between the white and black races which I believe will forever forbid the two races living together on terms of social and political equality. And in as much as they cannot so live, while they do remain together there must be the position of superior and inferior, and I as much as any other man am in favor of having the superior position assigned to the white race. I say upon this occasion I do not perceive that because the white man is to have the superior position the negro should be denied everything. I do not understand that because I do not want a negro woman for a slave I must necessarily want her for a wife. My understanding is that I can just let her alone"
Though he also said
"I should like to know, if taking this old Declaration of Independence, which declares that all men are equal upon principle, and making exceptions to it, where will it stop? If one man says it does not mean a negro, why may not another man say it does not mean another man? If that declaration is not the truth, let us get this statute book in which we find it and tear it out.
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."