When I entered the army I took forty-seven negroes into the army with me, and forty-five of them were surrendered with me. I said to them at the start: "This fight is against slavery; if we lose it, you will be made free."
Source, in full
Remark to some of his slaves at the start of the war (c. June 1861), recalled in an interview in Memphis, TN (Aug. 26, 1868), correspondence of the Cincinnati Commercial, reported in The New York Times (Sep. 3, 1868) p. 3, col. 4