When was the 13th ratified? And what is the President’s role in an amendment?
Lincoln had been calling for such an amendment for a while, but while it passed the senate, it couldn't pass in the house. In 1864, Lincoln pushed to have a call for the amendment added to the Republican platform. When he won the election and the Republicans gained seats in the house, it was able to pass. Lincoln signed the amendment, even though it was unnecessary and had never been done before to show his backing. Twenty-one states passed the amendment before Lincoln was assassinated.
December 1865. Seeing as though the amendment was made possible by the war and was foreseen by everyone (including Lincoln), it is quite reasonable to give him the credit.