MLA

Sykes, Christopher, 1907-1986. Waugh, Evelyn. Box 5, folder 129. 1962, undated. https://collections.library.yale.edu/catalog/10079852.

APA, 6th edition

Sykes, Christopher, 1907-1986. (["Box 5, folder 129"])(1962, undated)[Waugh, Evelyn]. https://collections.library.yale.edu/catalog/10079852.