MLA

Luhan, Mabel Dodge, 1879-1962. Donaldson, Hildegard. Box 9, folder 263. 1938-46, n.d.. https://collections.library.yale.edu/catalog/32195404.

APA, 6th edition

Luhan, Mabel Dodge, 1879-1962. (["Box 9, folder 263"])(1938-46, n.d.)[Donaldson, Hildegard]. https://collections.library.yale.edu/catalog/32195404.