MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 84, folder 1697-1698. 1923 Sep. https://collections.library.yale.edu/catalog/2039720.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 84, folder 1697-1698"])(1923 Sep)[Letters]. https://collections.library.yale.edu/catalog/2039720.