There are Ten Commandments in the Hebrew Bible. but people often add others, usually in jest. A popular Eleventh Commandment in the early 1800s was “Mind your business.” A political Eleventh Commandment from the 1960s is, “Thou shalt not speak ill of another Republican.”
 
“Keifer’s great sin, in the eyes of his fellow Republicans, was a violation of the eleventh commandment—“Thou shalt not get caught at it” was published in a Pennsylvania newspaper in April 1884. American entrepreneur George Francis Train (1829-1904) popularized this new eleventh commandment in a widely reprinted 1889 anecdote. “GEORGE FRANCIS TRAIN says that Boston’s Eleventh Commandment is, ‘Don’t get caught’” was published in the New York (NY) Herald on November 19, 1889.
 
 
Wikipedia: Ten Commandments
The Ten Commandments, also known as the Decalogue, are a set of biblical principles relating to ethics and worship, which play a fundamental role in Judaism, Christianity, and Islam. The commandments include instructions to worship only God, to honour one’s parents, and to keep the sabbath, as well as prohibitions against idolatry, blasphemy, murder, adultery, theft, dishonesty, and coveting. Different religious groups follow different traditions for interpreting and numbering them.
 
The Ten Commandments are listed twice in the Hebrew Bible, first at Exodus 20:1–17, and then at Deuteronomy 5:6–21.
 
Wikipedia: George Francis Train
George Francis Train (March 24, 1829 – January 5, 1904) was an American entrepreneur who organized the clipper ship line that sailed around Cape Horn to San Francisco; he also organized the Union Pacific Railroad and the Credit Mobilier in the United States in 1864 to construct the eastern portion of the Transcontinental Railroad, and a horse tramway company in England while there during the American Civil War.
   
26 April 1884, Saturday Evening Observer (Dunkirk, NY), pg. 4, col. 2:
KEIFER’S great sin, in the eyes of his fellow Republicans, was a violation of the eleventh commandment—“Thou shalt not get caught at it.”—Erie Herald.
 
19 November 1889, New York (NY) Herald, pg. 6, col. 4:
GEORGE FRANCIS TRAIN says that Boston’s Eleventh Commandment is, “Don’t get caught.”
 
26 November 1889, The Evening Repository (Canton, OH), “Brief and Terse,” pg. 2, col. 3:
George Francis Train says that he has been long enough in Boston to learn that the Eleventh COmmandment in that city is, “Thou shalt not get caught.”
 
13 January 1890, Evening Telegraph (Dixon, IL), pg. 1, col. 2:
George Francis Train says that Boston’s Eleventh Commandment is “Don’t get caught!”
 
22 February 1894, New York (NY) Times, pg. 9, col. 6:
“There should be an eleventh commandment: ‘Don’t get caught!’”
(George Francis Train writing to John Y. McKane.—ed.)
 
Old Fulton NY Post Cards
6 May 1894, Elmira (NY) Telegram, pg. 1, col. 6:
It was intimated that others, unlike himself (Colonel Breckenridge—ed.), had not violated the eleventh commandment—“Thou shalt not get caught.”
 
Chronicling America
4 February 1898, Kinsley (KS) Graphic, pg. 1, col. 3:
Senator Hanna always transacts his political business under fear of the unwritten commandment—“Thou shalt not get caught.”
 
Google News Archive
31 July 1908, Florence (AL) Times, pg. 5, col. 4:
...there will be much wine made, which comes right handy in a prohibition county, all you have to do is to obey the eleventh commandment, “Don’t get caught.”
   
2 November 1928, New York (NY) Times, pg. 24:
The Republicans have been caught. They have broken the Eleventh Commandment of politics.
   
Google News Archive
22 November 1951, Hendersonville (NC) Times-News, pg. 2, col. 2:
In short, it is the old eleventh commandment, “Don’t get caught.”
   
Time magazine
The Press: Keep the Rascal In
By Monday, Jul. 02, 1956
(...)
In short, by Texan Howerton’s generous code, there should be hope even for those who violate the eleventh commandment, i.e., “don’t get caught.”
 
Urban Dictionary
11th Commandment
Don’t get caught
(...)
by __SomeGuy__ August 16, 2010