The document is an approval for an appointment to the Treasury Department for Allen Gangewer, an abolitionist. The date on the document is April 11, 1865, the day that Lincoln gave his last public address and three days before he was fatally shot.

Gangewer was a newspaper editor and then served as private secretary to Salmon Chase, Lincoln's first Secretary of the Treasury and later a U.S. Supreme Court justice. Gangewer also had a hand in founding the National Colored Home, a Washington, D.C., facility that gave aid and shelter to African-Americans who had been enslaved.

The letter had sat in a desk belonging to another man, who recently died. When the man's wife went through the desk, she found the letter.

Auctioning the document will be the Raab Collection, based in Ardmore, Pa. The entity is known for its historical documents, including George Washington's original presidential address, Thomas Jefferson's letter bequeathing his personal library in order to found the Library of Congress, and a contract to noted astrophysicist Stephen Hawking for writing his first book.

The anticipated purchase for the Lincoln letter is $45,000.