MLA
Gonne, Maud, 1866-1953. Letter written by Maud Gonne to William Butler Yeats - September 9 [1903]. September 1903. 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/81289321j4-cor.
APA, 6th edition
Gonne, Maud, 1866-1953. (September 1903)[Letter written by Maud Gonne to William Butler Yeats - September 9 [1903]]. 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/81289321j4-cor.
Chicago
Gonne, Maud, 1866-1953, Letter written by Maud Gonne to William Butler Yeats - September 9 [1903], September 1903, 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/81289321j4-cor.