MLA

Speck, William A. (William Alfred), 1864-1928. AL (draft, incomplete) : Karlsbad?, to Adam Müller. Box 9, folder 290. 1807 Aug 28. https://collections.library.yale.edu/catalog/2005320.

APA, 6th edition

Speck, William A. (William Alfred), 1864-1928. (["Box 9, folder 290"])(1807 Aug 28)[AL (draft, incomplete) : Karlsbad?, to Adam Müller]. https://collections.library.yale.edu/catalog/2005320.