Lincoln never said anything like that. He avoided saying that. On the other hand, he said that so far as tested, black soldiers were as good as any, and of course he proposed voting rights for black soldiers.
Maybe he heard of this engagement:
"On the steaming night of June 6, 1863, four rebel regiments surprised black guards. The black novices, soldiers for only sixteen days, fumbled with their guns, fell back, stood firm, and flashed their bayonets. The blacks' white captain called the ensuing bayonet brawl "a horrible fight, the worst I was ever engaged in—not even excepting Shiloh."
In one ironic tableau, a Union black and a Confederate white lay slain, arms lodced like brothers, each with the other's bayonet planted in his belly. At last, a Union ship reinforced the unyielding blacks, and the rebels retreated. Black soldiers, declared an astounded Confederate battle report, resisted us "with considerable obstinacy, while the white or true Yankee portion ran like whipped curs."
One Confederate master suffered the best proof of black obstinacy. His slave captured him "and brought him into camp with great gusto." A Wisconsin cavalry officer described the lesson many Northerners learned from Fort Wagner and Milliken's Bend (and from the battle for Port Hudson, Louisiana, where black troops futilely charged and their bodies were left to rot under the blazing sun), "I never believed in niggers before, but by Jasus, they are hell for fighting."
--"The South vs. the South" p. 127 by William Freehling.
Walt