MLA

Barrie, J. M. (James Matthew), 1860-1937. "Fairy". Box 42, folder 910. 1903 October 14. https://collections.library.yale.edu/catalog/2008280.

APA, 6th edition

Barrie, J. M. (James Matthew), 1860-1937. (["Box 42, folder 910"])(1903 October 14)["Fairy"]. https://collections.library.yale.edu/catalog/2008280.