If the Bible approves slavery and Abraham Lincoln fought to abolish slavery what was Lincoln's Religion?

Abraham Lincoln's father was a Baptist, but Lincoln himself was never known to have claimed to be of the Baptist faith. He did attend a Presbyterian Church while serving as President, but never formally joined any particular church. But the Bible does not approve of slavery, however it does not condemn it either. In fact, in the Old Testament, it informs Jewish slave owners on how to treat slaves. Abraham owned a slave.