MLA

Berberova, N. (Nina), 1901-1993. Budberg, Moura. Box 5, folder 98. n.d. https://collections.library.yale.edu/catalog/16687988.

APA, 6th edition

Berberova, N. (Nina), 1901-1993. (["Box 5, folder 98"])(n.d)[Budberg, Moura]. https://collections.library.yale.edu/catalog/16687988.