George Washington to Nicholas Cooke, 3 April 1776

A letter from George Washington to Nicholas Cooke, Governor of Rhode Island telling him the courier carries letter to Congress: "the post which conveys this to you Carrys letters of importance to Congress, I therefore request, that you will give him positive orders to avoid going by any road, where there may be the least danger of his being intercepted by the enemy"
Collected in Henry Wadsworth Longfellow Dana Papers, Miscellaneous Famous People.