MLA
Commission, United States Christian. Letter of Invitation to the United States Christian Commission (Philadelphia, Pennsylvania) Regarding Work of the Christian Commission with the Union Army - April 30, 1864. 1864. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 23, Folder 32. https://digital.library.emory.edu/purl/7203xsj56v-cor.
APA, 6th edition
Commission, U. S. C. (1864). Letter of invitation to the United States Christian Commission (Philadelphia, Pennsylvania) regarding work of the Christian Commission with the Union Army - April 30, 1864 (Box 23, Folder 32) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/7203xsj56v-cor.
Chicago
Commission, United States Christian. “Letter of Invitation to the United States Christian Commission (Philadelphia, Pennsylvania) Regarding Work of the Christian Commission with the Union Army - April 30, 1864.” Letters (correspondence). Civil War Collection, 1864. Box 23, Folder 32. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/7203xsj56v-cor.