A hastily written letter from President Lincoln to Gen. George B. McClellan to check on his progress in chasing down the retreating Confederates after the Battle of Antietam sold for $100,000 in less than a day of it going on the market, according to a spokesman for the Raab Collection in Philadelphia.

Letters signed by Lincoln are highly prized and considered very collectible.

The buyer, who purchased the letter early this morning, was only identified as a private collector and businessman living in the Dakotas, who loves Lincoln and is relatively new to the collecting of original documents of the Civil War, the spokesman said.

The letter, written on Oct. 29, 1862, is believed to be the last letter from Lincoln to McClellan before the President fired him for delaying his pursuit of the Confederates following the Union victory at Sharpsburg on Sept. 18.