Behind that simple statement lies one of the sensational and controversial fights in history. Durán’s reputation was built on his ferocity as a boxer, a fighter so fierce he was nicknamed "Manos de Piedra" by Panamanian broadcaster Alfonso Castillo. The phrase translates as "hands of stone".

Trainer Ray Arcel once asked: "If you walked into a ring or met him in a dark alley would you be afraid? So would I!"

Yet in the eighth round that night in New Orleans, Durán gestured to the referee that he was unwilling to continue the fight. It was a moment that haunts him still.

The beginning of the 1980s was a time when Muhammad AlI's career was coming to a less than glorious end.

The emergence of Mike Tyson was a few years away and so focus shifted from the heavyweights to the lighter weight divisions.

Durán and Leonard, "Marvellous" Marvin Hagler and Thomas "the hit man" Hearns constituted a group known as the "Fabulous Four", or in the words of Boston Herald columnist George Edward Kimball III, the "Four Kings".

Roberto Durán Samaniego had been raised in poverty in Panama City and had his first professional contest in 1968 when he was still only 16 years of age. In 1972, at New York’s Madison Square Garden, he beat Scottish boxer Ken Buchanan in a controversial fight to lift the World Boxing Association (WBA) lightweight belt, though eventually he gave up the title for a crack at Sugar Ray.

Leonard had won gold at the 1976 Olympics in Montreal. After turning professional the following year he remained unbeaten and in November 1979, he beat Wilfred Benitez to become WBC welterweight champion.

In June 1980 he returned to the city of his Olympic triumph to fight Durán. Leonard’s record at the time was 26 victories, of which 18 had been by knockout.

"Leonard Durán I" went the distance, which in those days was 15 rounds. When it was over, the judges gave it to Durán on a unanimous decision.

When Durán returned home to Panama after the fight, it is said that 700,000 turned out to welcome him back as he travelled through the streets in a motorcade.

Leonard for his part briefly contemplated retirement. "I’ve never been hurt so much in my career, his fists felt like rocks," he said.

Yet he very soon sought a rematch and trained with a sparring partner who replicated Durán’s style.

The second encounter came only 158 days after their first meeting and was held at the New Orleans Superdome. The fight was staged by the extrovert promoter Don King.

Durán had celebrated his June victory with some enthusiasm and a succession of parties. His weight had ballooned and he was out of condition. This meant he was obliged to lose around 20 kilos in little more than a month.

In his autobiography, published in 2016, Durán said: "I felt sick from when I started training and stayed that way until the fight. I spent almost every day in the sauna and went two days without eating. I was too weak and could not feel my legs. There was no trace of the boxer from a few months before."

At the pre-fight press conferences, Durán had hurled insults at Leonard.

At training, Leonard had put on a false beard to complain that Durán’s facial hair had protected him in the first fight.

The New York Times once described Durán having "the sneering snarl of a Caribbean pirate".

In Leonard’s corner for the rematch was Muhammad Ali’s legendary trainer Angelo Dundee, who later recalled the atmosphere in the moments building up to the fight.

"We were sky-high in the dressing room. Different from last time. Everything was cool, smooth, good," he said.

Leonard seemed relaxed when singer Ray Charles also entered the ring. Charles performed "America the Beautiful" and then made his way across the ring to embrace Leonard.

By the seventh round, Leonard was on top and taunting his opponent.

Then in the eighth, with less than 30 seconds of the round left, Durán held up his arm to end the fight.

His gesture was not immediately understood by referee Octavio Meyran, who originally signalled for the fighters to continue. A few seconds later, the message did get through. Leonard raced away in celebration.

It has gone down in folklore that Durán used the words Spanish words "No mas" to indicate the fight was over, yet Durán has always maintained that he never used the words.

"I never said ‘no mas.’ I just turned my back and motioned to the referee that I didn’t want to continue," he wrote in his autobiography. 

"When the referee asked me what I was doing, all I said was ‘no sigo [I do not follow]." I couldn’t go on. I couldn’t keep fighting. I felt like crap. But I never said ‘no mas.’"

Leonard insists he never heard the words either, but that was hardly surprising, such was the noise in the ring. A review of the fight tape offers no clarification.

In 2016, a biopic entitled "Hands of Stone" told Durán's story.

Duran’s son Robin later said: "It’s very hard for a fighter to speak with a mouthpiece on. He just waved his hand."

There were also suggestions that the words may have been used by Meyran or Ray Arcel, or even that the legend was started by television commentator Howard Cosell.

Whatever the words used, the decision to give up had implications for Durán.

In The Ring magazine, boxing historian Bert Sugar wrote: "It was thought there were but four immutable laws which governed the universe: That the Earth always goes around the sun; That lawyers always get paid first; That every action has an equal and opposite reaction; And that Roberto Durán would have to be carried out on his shield, blood streaming out of his ears, before he would ever quit. Now you can scratch one of the above."

The Louisiana State Athletic Commission immediately fined Durán $7,500 for what they described as an "unsatisfactory performance". They even tried to suspend his share of the purse and when Durán returned home this time, there was no cavalcade of triumph through the streets.

"He became a pariah," said boxing promoter Bob Arum.

Durán’s daughter Irichelle later told Fox Sports: "I think he felt like he betrayed the people here."

Sports Illustrated writer Bill Nack perfectly summed up Durán’s fall from grace. "If Durán arrived in New Orleans with a reputation as unassailable as Simón Bolívar's, he left with it somewhere in the neighborhood of Papa Doc's."

Newspaper and television advertisements were summarily dropped in Panama and for a while Durán was largely shunned. "I didn’t even leave my house, everybody was making fun of me," Durán said. He was dropped by his trainer and by his promoter.

A brief retirement and unsuccessful challenge for the WBC super welterweight title did nothing to lift the mood.

Encouraged by his wife, he returned to the ring once and on his 32nd birthday, he stopped American Davey Moore in eight rounds to lift the WBA super welterweight belt at Madison Square Garden.

Sports Illustrated magazine headlined their cover: "Redemption for Roberto - Erasing the Shame of No Mas."

Another regal welcome in Panama City indicated that he was the favourite son once again. He was not alone in reflecting that he was now lauded by many of those who had shunned him.

His charitable acts towards the poor in his homeland became almost as legendary as his reputation as a fighter. It is said that he named his son after Robin Hood.

Durán fought Leonard a third time in 1989 and lost again but his boxing career lasted until 2001, by which time he had won world titles at four different weights. Leonard won titles in five different divisions.

The following year, The Ring drew up a ranking of the greatest since the magazine was first published in 1922. Durán was number five, Leonard was number eight.

When Durán was diagnosed with COVID-19 earlier this year, Leonard recorded a video message in which he told Durán: "You’ll pull through champ. You’re the best."

Durán was released from hospital after treatment and told medical staff: "I am a former world champion but you are the true champions of life."