MLA

Stieglitz, Alfred, 1864-1946. Kandinsky, Wassily. Box 26, folder 627. 1913, n.d.. https://collections.library.yale.edu/catalog/10575553.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 26, folder 627"])(1913, n.d.)[Kandinsky, Wassily]. https://collections.library.yale.edu/catalog/10575553.