MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 63, folder 1439-1441. 1926 Aug-Sep. https://collections.library.yale.edu/catalog/2039844.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 63, folder 1439-1441"])(1926 Aug-Sep)[Letters]. https://collections.library.yale.edu/catalog/2039844.