US Senator William Edgar Borah, writing in The Reader's Digest, Vol. 8, Issue 2 (1929), p. 776; this has only rarely begun to be attributed to Washington, since about 2010.
Misattributed
George Washington: Zitate auf Englisch (seite 8)
George Washington war erster Präsident der Vereinigten Staaten von Amerika. Zitate auf Englisch.“It is infinitely better to have a few good men than many indifferent ones.”
Letter to James McHenry (10 August 1798)
1790s
Letter to John Armstrong, 11 March 1782, in Ford's Writings of George Washington (1891), vol. XII, p. 111. This is frequently attached to part of a letter to Brigadier-General Nelson of 20 August 1778, as in this 1864 example from B. F. Morris, The Christian Life and Character of the Civil Institutions of the United States, pp. 33-34:
I am sure that there never was a people who had more reason to acknowledge a divine interposition in their affairs than those of the United States; and I should be pained to believe that they have forgotten that agency which was so often manifested during the Revolution, or that they failed to consider the omnipotence of that God who is alone able to protect them. He must be worse than an infidel that lacks faith, and more than wicked that has not gratitude enough to acknowledge his obligations.
1780s
Letter to General Armstrong (26 March 1781) http://www.greatseal.com/mottoes/coeptis.html, as quoted in The Religious Opinions and Character of Washington (1836) by Edward Charles McGuire, p. 122
1780s
To John Hancock https://web.archive.org/web/20141008220806/http://amrevmuseum.org/reflections/african-americans-continental-army-and-state-militias-during-american-war-independence (31 December 1775)
1770s, Letter to John Hancock (1775)
“We had quitters during the Revolution too… we called them "Kentuckians."”
This attribution apparently originated with a statement of a cartoon version of Washington on an episode http://www.imdb.com/title/tt0701155/quotes of The Simpsons. Though not initially presented as a genuine quote this has sometimes been attributed to Washington.
Misattributed, Spurious attributions
Message to the U.S. Congress (9 July 1789); The Writings of George Washington: Being His Correspondence, Addresses, Messages, and Other Papers, Official and Private (1837) edited by Jared Sparks, p. 159 (PDF) http://books.google.com/books?vid=OCLC29437768&id=qy2nqT6FnLMC&pg=RA1-PA159&lpg=RA1-PA159&dq=%22carrying+these+into+effect,+fidelity+and+diligence%22&num=100
1780s
1790s, Farewell Address (1796)
First Annual Address, to both House of Congress (8 January 1790)
1790s
1780s, The Newburgh Address (1783)
1770s, Letter to Phyllis Wheatley (1776)
Attributed to George Washington, John Bernard, Retrospections of America, 1797–1811, p. 91 (1887). This is from Bernard's account of a conversation he had with Washington in 1798. Reported as unverified in Respectfully Quoted: A Dictionary of Quotations (1989).
Posthumous attributions
Letter to U.S. Attorney General http://memory.loc.gov/cgi-bin/query/r?ammem/mgw:@field(DOCID+@lit(gw300376)) Edmund Randolph (28 September 1789), as published in The Writings of George Washington from the Original Manuscript Sources, 1745-1799 edited by John C. Fitzpatrick
The inscription on the facade of the New York Supreme Court court house in New York County is a misquotation from the above letter: "The true administration of justice is the firmest pillar of good government." See "George Denied His Due" by Bruce Golding, in The New York Post (16 February 2009) http://www.nypost.com/seven/02162009/news/regionalnews/george_denied_his_due_155401.htm
1780s
Letter to Mrs. George William Fairfax (12 September 1758)
1750s
Letter to Edmund Pendleton (22 January 1795)
1790s
http://www.bartleby.com/43/24.html
1790s, Farewell Address (1796)
1790s, Farewell Address (1796)
Letter to the Protestant Episcopal Church (19 August 1789) Scan at American Memory (Library of Congress). http://memory.loc.gov/mss/mgw/mgw2/038/0580042.jpg
1780s
1790s, Farewell Address (1796)
1780s, The Newburgh Address (1783)