MLA

Wallace, Lew, 1827-1905. Letter : Crawfordsville, Indiana, to [Benn?] Pitman. Box 20, folder GROUP 426, F-2. 1863 [i.e. 1864] Jan 5. https://collections.library.yale.edu/catalog/2014449.

APA, 6th edition

Wallace, Lew, 1827-1905. (["Box 20, folder GROUP 426, F-2"])(1863 [i.e. 1864] Jan 5)[Letter : Crawfordsville, Indiana, to [Benn?] Pitman]. https://collections.library.yale.edu/catalog/2014449.