APA (7th ed.) Citation

Lincoln, M. T., Barton, W. E., & William E. Barton Collection of Lincolniana. (1864). Letter: Washington, D.C., to Benjamin F. Butler, [Headquarters, Army of the Potomac].

Chicago Style (17th ed.) Citation

Lincoln, Mary Todd, William E. Barton, and William E. Barton Collection of Lincolniana. Letter: Washington, D.C., to Benjamin F. Butler, [Headquarters, Army of the Potomac]. 1864.

MLA (8th ed.) Citation

Lincoln, Mary Todd, et al. Letter: Washington, D.C., to Benjamin F. Butler, [Headquarters, Army of the Potomac]. 1864.