MLA

Turgenev, Ivan Sergeevich, 1818-1883. Letter : Moscow, to Pauline Viardot. Box 28, folder GROUP 522, F-1. 1879 Mar [14?]. https://collections.library.yale.edu/catalog/32600853.

APA, 6th edition

Turgenev, Ivan Sergeevich, 1818-1883. (["Box 28, folder GROUP 522, F-1"])(1879 Mar [14?])[Letter : Moscow, to Pauline Viardot]. https://collections.library.yale.edu/catalog/32600853.