MLA
Gonne, Maud, 1866-1953. Letter written by Maud Gonne to William Butler Yeats - September 28 [1927]. September 28, 1927. 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/1676t1g3wh-cor.
APA, 6th edition
Gonne, Maud, 1866-1953. (September 28, 1927)[Letter written by Maud Gonne to William Butler Yeats - September 28 [1927]]. 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/1676t1g3wh-cor.
Chicago
Gonne, Maud, 1866-1953, Letter written by Maud Gonne to William Butler Yeats - September 28 [1927], September 28, 1927, 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/1676t1g3wh-cor.