Any recommendations on a book about William O. Stoddard?

[LincolnMan]

Roger, I love that quote and hope Lincoln said it as well. While I was looking up something else, I came across a Stoddard reference in Sandburg's One Volume Edition of Abraham Lincoln. On page 328 of the book, the aftermath of Fredericksburg is talked about. It is mentioned that Lincoln issued an address to the soldiers of the Army of the Potomac to try and encourage them after their defeat in the battle. According to Sandburg, Stoddard then wrote something about Lincoln that we are all familiar with regarding the losses: "We lost fifty per cent more men than did the enemy, and yet there is the sense in the awful arithmetic propounded by Mr. Lincoln. He says that if the same battle were to be fought over again, every day, through a week of days, with the same relative results, the army under Lee would be wiped out to its last man, the Army of the Potomac would still be a mighty host, but the war would be over, the Confederacy gone. No general yet found can face the arithmetic, but the end of the war will be at hand when he shall be discovered." Do we owe this knowledge of what Lincoln said to Stoddard? Or do we have it also from another source?