Originally attributed to the “Rev. Jonas Clarke or one of his company” in “No King But King Jesus” (2001) ( cache at Internet Archive http://web.archive.org/web/20010422194315/www.truthinhistory.org/NoKing.htm) by Charles A. Jennings on his website Truth in History http://www.truthinhistory.org, and subsequently attributed to Adams in books like Is God with America? (2006) by Bob Klingenberg, p. 208, and Silenced in the Schoolhouse (2008) by Michael Williams, p. 5. (The mistake may have come about because John Adams and John Hancock are mentioned in Jennings' account immediately before Clark.) This is supposed to have been said in reply to Major Pitcairn's demand to “Disperse, ye villains, lay down your arms in the name of George the Sovereign King of England.” Clark's own account http://books.google.com/books?id=9S8eAAAAMAAJ&pg=PA6#v=onepage&q&f=false makes no mention or this (or any other) reply, however. “No king but King Jesus” was the slogan of the Fifth Monarchists https://en.wikipedia.org/wiki/Fifth_Monarchists during the Interregnum in England, but there is little evidence for its use during the American Revolution.
Misattributed
