Thomas Jefferson, Henry Augustine Washington (1854). “The Writings of Thomas Jefferson: Being His Autobiography, Correspondence, Reports, Messages, Addresses, and Other Writings, Official and Private : Published by the Order of the Joint Committee of Congress on the Library, from the Original Manuscripts, Deposited in the Department of State”, p.591
Matthew Barnett (2011). “The Cause within You: Finding the One Great Thing You Were Created to Do in This World”, p.177, Tyndale House Publishers, Inc.