John Adams' letter to Benjamin Rush (December 21, 1809), as quoted in "No, Mr. Beck, John Adams Did Not Think Governments Must Be Administered by the Holy Ghost" by Chris Rodda, www.huffingtonpost.com. June 16, 2010.
John Adams, Abigail Adams, Thomas Jefferson (1971). “The Adams-Jefferson letters: the complete correspondence between Thomas Jefferson and Abigail and John Adams”, Touchstone