MLA
Gonne, Maud, 1866-1953. Letter written by Maud Gonne to William Butler Yeats - August 5 [1920]. August 5, 1920. Maud Gonne and W.B. Yeats Papers, circa 1890-1938. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/255z612n00-cor.
APA, 6th edition
Gonne, Maud, 1866-1953. (August 5, 1920)[Letter written by Maud Gonne to William Butler Yeats - August 5 [1920]]. Maud Gonne and W.B. Yeats Papers, circa 1890-1938, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/255z612n00-cor.
Chicago
Gonne, Maud, 1866-1953, Letter written by Maud Gonne to William Butler Yeats - August 5 [1920], August 5, 1920, Maud Gonne and W.B. Yeats Papers, circa 1890-1938, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/255z612n00-cor.