Question: When did Cassius Marcellus Clay fight against Elmo Henderson?

Context paragraphs:
Muhammad Ali vs. Sonny Liston: The two fights between Muhammad Ali and Sonny Liston for boxing's World Heavyweight Championship were among the most anticipated, watched and controversial fights in the sport's history. " Sports Illustrated" magazine named their first meeting, the Liston–Clay fight (Ali had not yet changed his name from Cassius Clay), as the fourth greatest sports moment of the twentieth century.

Facing Ali: Facing Ali is a 2009 documentary directed by Pete McCormack about Muhammad Ali (born Cassius Marcellus Clay, Jr. in Louisville, Kentucky) as told from the perspectives of some of the notable opponents he faced during his career: George Chuvalo, Sir Henry Cooper, George Foreman, "Smokin'" Joe Frazier, Larry Holmes (a former sparring partner of Ali), Ron Lyle, Ken Norton, Earnie Shavers, Leon Spinks and Ernie Terrell.

Cassius Marcellus Clay Sr.: Cassius Marcellus Clay (November 11, 1912 – February 8, 1990) was an American painter and musician.  He was the father of three-time World Heavyweight Champion Muhammad Ali and Rahman Ali, and the grandfather of Laila Ali.  He married Odessa Lee O'Grady in the 1930s and worked as a painter and a musician.  He was described as "a handsome, mercurial, noisy, combative failed dreamer" and a "hard-drinking, skirt-chasing dandy of a daddy".  His son Muhammad Ali described him as "the fanciest dancer in Louisville".

Brutus J. Clay: Brutus Junius Clay (July 1, 1808 – October 11, 1878) was a U.S. Representative from Kentucky, and a son of Green Clay.  His brother Cassius Marcellus Clay also was a politician in the state, and they both joined the Unionist Party at the time of the American Civil War.

Muhammad Ali: Muhammad Ali ( ; born Cassius Marcellus Clay Jr.; January 17, 1942 – June 3, 2016) was an American professional boxer and activist.  He is widely regarded as one of the most significant and celebrated sports figures of the 20th century.  From early in his career, Ali was known as an inspiring, controversial, and polarizing figure both inside and outside the ring.

Botherum: Botherum was built for Madison C. Johnson in 1850 or 1851 (sources vary) by John McMurtry, a well-known architect and builder based in Lexington.  The house was intended, in part, as a shrine to Johnson's late wife Sally Ann, a sister of Cassius Marcellus Clay who died giving birth in 1828.

Elmo Henderson: Elmo Henderson born April 8, 1935 is an African-American former boxer from Texas.  Despite his dubious claim of a 1972 win against Muhammad Ali in an exhibition match in San Antonio, Texas, he did not become particularly well known in the boxing community; John Spong of the "Texas Monthly" said that the match was the "shot not heard round the world".  However, people who attended the exhibition say Elmo Henderson did not defeat Ali, and newspaper reports after the exhibition made no mention of Ali losing.  After the match, Henderson became a part of George Foreman's Rumble in the Jungle event in Zaire and won a libel suit against Norman Mailer and "Playboy".  As of 2003, Henderson was a homeless man in Austin, Texas.  As of 2015, Henderson lives in a care home in Northern California.

The Soul of a Butterfly: The Soul of a Butterfly is the autobiography of Muhammad Ali, born Cassius Marcellus Clay Jr., a former heavyweight boxer who was a three time World Heavyweight Champion and is the greatest heavyweight of all time.

Cassius Marcellus Clay (politician): Cassius Marcellus Clay ( ; October 19, 1810 – July 22, 1903), nicknamed the "Lion of White Hall", was a Kentucky planter, politician, and emancipationist who worked for the abolition of slavery.  He freed the slaves that were handed down as his inheritance from his father.  Those freed slaves were allowed to stay and were paid a wage.  He was appointed by President Abraham Lincoln as the United States minister to Russia during the American Civil War, and is credited with gaining Russian support for the Union.

Odessa Grady Clay: Odessa Lee Clay (née O'Grady; February 12, 1917 – August 20, 1994) was the mother of three-time World Heavyweight Champion Muhammad Ali and Rahman Ali, and the grandmother of Laila Ali.  She married Cassius Marcellus Clay, Sr. in the 1930s and worked for some time as a household domestic to help support her young children.

Supporting paragraphs: Elmo Henderson Muhammad Ali
Answer: 1972