MLA
Gonne, Maud, 1866-1953. Letter written by Maud Gonne to William Butler Yeats - [January?] 12 [1898?]. January 12, 1898. 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/26663xsm5p-cor.
APA, 6th edition
Gonne, Maud, 1866-1953. (January 12, 1898)[Letter written by Maud Gonne to William Butler Yeats - [January?] 12 [1898?]]. 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/26663xsm5p-cor.
Chicago
Gonne, Maud, 1866-1953, Letter written by Maud Gonne to William Butler Yeats - [January?] 12 [1898?], January 12, 1898, 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/26663xsm5p-cor.