September 17, 1859: Speech at Cincinnati, Ohio
I think Slavery is wrong, morally, and politically. I desire that it should be no further spread in these United States, and I should not object if it should gradually terminate in the whole Union.I say that we must not interfere with the institution of slavery in the states where it exists, because the constitution forbids it, and the general welfare does not require us to do so.
http://www.nps.gov/liho/historyculture/slavery.htm
The basic source of conflict during the 1850s concerned the extension of slavery in U.S. territorial possessions, not the abolition of slavery within the states.