John Sell's letter to his brother
The letter displayed to the right is from the John M. Sell Civil War Collection. John Sell wrote numerous letters to his brother Willie while serving in the Civil War. If you cite more than one you might include the date of each to differentiate it from the others:
(John Sell to William Sell, 3 November 1861)
If you cited only one letter from the collection, you might omit the date:
(John Sell to William Sell)
See the MLA Handbook pages 54-58 for more information.