MLA
Early, John, 1786-1873. Letter from John Early (Lynchburg, Virginia) to Robert Paine (Aberdeen, Mississippi) - July 13, 1859. July 13, 1859. Robert Paine Papers, 1828-1882. Pitts Theology Library. https://digital.library.emory.edu/purl/0278sf7n5h-cor.
APA, 6th edition
Early, John, 1786-1873. (July 13, 1859)[Letter from John Early (Lynchburg, Virginia) to Robert Paine (Aberdeen, Mississippi) - July 13, 1859]. Robert Paine Papers, 1828-1882, Pitts Theology Library. https://digital.library.emory.edu/purl/0278sf7n5h-cor.
Chicago
Early, John, 1786-1873, Letter from John Early (Lynchburg, Virginia) to Robert Paine (Aberdeen, Mississippi) - July 13, 1859, July 13, 1859, Robert Paine Papers, 1828-1882, Pitts Theology Library. https://digital.library.emory.edu/purl/0278sf7n5h-cor.