Any recommendations on a book about William O. Stoddard?

[RJNorton]

Bill mentioned Francis Carpenter. In his book on pp. 258-259, Carpenter includes one of my favorite Lincoln quotes: "If I were to try to read, much less answer, all the attacks made on me, this shop might as well be closed for any other business. I do the very best I know how - the very best I can; and I mean to keep doing so until the end. If the end brings me out all right, what's said against me won't amount to anything. If the end brings me out wrong, ten angels swearing I was right would make no difference."

An almost identical version was given by Abram J. Dittenhoeffer, a New York lawyer, who claimed to have frequent meetings with Lincoln. In their book, Don and Virginia Fehrenbacher give Dittenhoeffer's version a "D" which means "a quotation about whose authenticity there is more than average doubt."

According to Carpenter, Lincoln uttered the quote in reaction to a verbal attack on him from the Committee on the Conduct of War. Dittenhoeffer's account is that the quote was Lincoln's response to criticism of his reconstruction policy.

I would like to believe this is an authentic Lincoln quote. Has anyone else come across this quote in another source?