MLA
Special Order No. 20 (Extract) from the United States War Department, Adjutant General's Office (Washington, D.C.) Honorably Discharging Corporal Gardner A. Kimball from the 1st Massachusetts Volunteers to Allow Him to Enlist in the United States Colored Troops - January 14, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 23, Folder 35. https://digital.library.emory.edu/purl/679573n77c-cor.
APA, 6th edition
Special Order No. 20 (Extract) from the United States War Department, Adjutant General's Office (Washington, D.C.) honorably discharging Corporal Gardner A. Kimball from the 1st Massachusetts Volunteers to allow him to enlist in the United States Colored Troops - January 14, 1864 (Box 23, Folder 35). (1864). [Orders (military records)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/679573n77c-cor.
Chicago
“Special Order No. 20 (Extract) from the United States War Department, Adjutant General's Office (Washington, D.C.) Honorably Discharging Corporal Gardner A. Kimball from the 1st Massachusetts Volunteers to Allow Him to Enlist in the United States Colored Troops - January 14, 1864.” Orders (military records). Civil War Collection, 1864. Box 23, Folder 35. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/679573n77c-cor.