When his Christian friends at Petersburg interfered to prevent his proposed duel with Shields and told him that it was contrary to the teachings of the Bible and Christianity he remarked, "The Bible is not my book nor Christianity my profession" (Letter of W Perkins).
While at Washington in a letter to his old friend, Judge Wakefield written in 1862 in answer to inquiries respecting his belief and the expressed hope that he had become convinced of the truth of Christianity, he replied as follows,
"My earlier views of the unsoundness of the Christian scheme of salvation and the human origin of the Scriptures have become clearer and stronger with advancing years and I see no reason for thinking I shall ever change them."
In a discussion touching upon the paternity of Jesus, he said, "There must have been sexual intercourse between man and woman and not between God and his daughter." The above words were uttered in the presence of Mr Green Caruthers and Mr WA Browning of Springfield. Lincoln contended that Jesus was either the son of Joseph and Mary or the illegitimate son of Mary.
The following was a favorite maxim with him: "What is to be will be and no prayers of ours can arrest the decree."(Statement of Mrs Lincoln).
In a speech on Kansas delivered in 1856, he used the following words in regard to Providence: "Friends I agree with you in Providence but I believe in the Providence of the most men, the largest purse, and the longest cannon" (Lincoln's Speeches p 140).
Source: John Eleazer Remsburg, Abraham Lincoln Was He a Christian? (Truth Seeker Co., 1893), 291-309.