MLA
Keener, John Christian, 1819-1906. Letter from John Christian Keener (New Orleans, Louisiana) to Robert Paine (Aberdeen, Mississippi) - October 24, 1881. October 24, 1881. Robert Paine Papers, 1828-1882. Pitts Theology Library. https://digital.library.emory.edu/purl/815p8czb3b-cor.
APA, 6th edition
Keener, John Christian, 1819-1906. (October 24, 1881)[Letter from John Christian Keener (New Orleans, Louisiana) to Robert Paine (Aberdeen, Mississippi) - October 24, 1881]. Robert Paine Papers, 1828-1882, Pitts Theology Library. https://digital.library.emory.edu/purl/815p8czb3b-cor.
Chicago
Keener, John Christian, 1819-1906, Letter from John Christian Keener (New Orleans, Louisiana) to Robert Paine (Aberdeen, Mississippi) - October 24, 1881, October 24, 1881, Robert Paine Papers, 1828-1882, Pitts Theology Library. https://digital.library.emory.edu/purl/815p8czb3b-cor.