American boxer Muhammad Ali (1942-2016) said in his autobiography The Greatest: My Own Story (1975):
 
“Champions aren’t made in gyms. Champions are made from something they have deep inside them—a desire, a dream, a vision. They have to have last minute stamina, they have to be a little faster, they have to have the skill and the will. But the will must be stronger than the skill.”
 
“The will must be stronger than the skill” has been frequently quoted.
 
   
Wikipedia: Muhammad Ali
Muhammad Ali (/ɑːˈliː/; born Cassius Marcellus Clay, Jr., January 17, 1942 – June 3, 2016) was an American professional boxer, generally considered one of the greatest heavyweights in the history of the sport. Early in his career, Ali was known for being a controversial and polarizing figure both inside and outside the boxing ring. He was one of the most recognized sports figures of the past 100 years, crowned “Sportsman of the Century” by Sports Illustrated and “Sports Personality of the Century” by the BBC.
       
OCLC WorldCat record
The greatest, my own story
Author: Muhammad Ali; Richard Durham
Publisher: New York : Random House, ©1975.
Edition/Format:   Print book : Biography : English : 1st ed
Database: WorldCat
Summary:
Heavyweight boxing champ and outrageous poet, Muhammad Ali reveals the man behind the gloves.
 
11 August 1976, Sentinel-Enterprise (Fitchburg, MA) “Book Look” by Rick Bause, pg. 20, col. 1:
“Champions are made,” says the Champ, “from something they have deep inside them—a desire, a dream, a vision. They have to have last minute stamina, they have to be a little faster, they have to have the skill and the will. But the will must be stronger than the skill.”
 
Muhammad Ali’s “The Greatest” does not come highly recommended, even for the staunchest of fight fans.
   
Google Books
Reaching for Excellence:
The Glory and Decay of Sport in India
By Melville De Mellow
New Delhi: Kalyani Publishers
1979
Pg. 59:
“Champions are not made in gyms. Champions are made from something they have deep inside them — a desire, a dream, a vision. They have to have stamina. They have to be a little faster. They have to have the skill and the will, but the will must be stronger than the skill”.
(From Muhammad Ali’s The Greatest.—ed.)
 
26 January 1986, The Times of India (New Delhi), ““More Will Than Skill” by Road Runner, pg. A7, col. 8:
At this level the will has to be stronger than the skill.
   
Google Books
The Reader’s Digest
Volume 152
1998
Pg. 180:
They have to have last- minute stamina, they have to be a In de faster, they have to have the skill and the will. But the will must be stronger than the skill. -The Greatest (Random House)
 
Google Books
The Big Book of Business Quotations
By Editors Of Perseus Publishing
New York, NY: Basic Books
2003
Pg. 369:
Champions aren’t made in gyms. Champions are made from something they have deep inside them— a desire, a dream, a vision. They have to have the skill, and the will. But the will must be stronger than the skill. Muhammad Ali (b. 1942) U.S. boxer. The Greatest (1975)
 
ESPN.com
Muhammad Ali’s 10 best quotes
September 4, 2016 12:38 AM ET
Darren Rovell
ESPN Senior Writer
(...)
6. “The will must be stronger than the skill.”
Why we love it: Ali was undoubtedly an incredible athlete who was uniquely talented. But it’s also undeniable that no one believed in Ali more than he did himself. Seemingly willing himself to some victories, Ali owes part of record to his self-confidence—beyond just his ability to move and punch.
 
Twitter
Marc Mendelson
‏@SouthAfricanASP
Muhammad Ali: “Champions have to have the skill & the will. But the will must be stronger than the skill.” Important in search 4 #AMR Champs
2:38 AM - 4 Jun 2016