As the faithful chanted a Muslim prayer in unison, dignitaries and fans stood shoulder to shoulder to honor a man who used his celebrity to push for peace among races, religions and cultures.
On phones and screens around the globe, thousands more joined the service from afar through streams and broadcasts, watching a traditional Muslim funeral ceremony play out for one of their heroes.
The prayer service Thursday, known as Jenazah, began two days of memorials that Ali crafted himself in exacting detail years before his death Friday. He designed them with the intent to make them open to the world and to offer a view into a faith many Americans know little about.
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"Ali was the people's champion and champion he did the cause of his people," said Sherman Jackson, a Muslim scholar who spoke at the service. Jackson said Ali did more to normalize the Islamic faith than anyone else, both in his life and in his death.
"Ali made being a Muslim cool," he said. "Ali made being a Muslim dignified."
More than 14,000 got tickets for the Thursday service in Ali's hometown of Louisville. Some traveled thousands of miles to attend. Civil rights activist Jesse Jackson, boxing promoter Don King, former boxer Sugar Ray Leonard and Louis Farrakhan, head of the Nation of Islam, were among the high-profile guests in attendance. Ali joined the Nation of Islam, the black separatist religious movement, in the 1960s. He left after a decade in favor of mainstream Islam, which emphasizes an embrace of all races and ethnicities.
Ali insisted he wanted the traditional Muslim ceremony to be open to all, organizers said.
The attendees were young and old; black and white; Muslims, Christians and Jews. Some wore traditional Islamic clothing, others blue jeans or business suits. Outside the arena, millions more were able to watch. The term "Jenazah" trended on Twitter as the service started.
"We welcome the Muslims, we welcome the members of other faith communities, we welcome the law enforcement community," Imam Zaid Shakir told the crowd at the start of the service. "We welcome our sisters, our elders, our youngsters."
"All were beloved to Muhammad Ali."
The service lasted less than an hour. There was no stage or altar. Speakers stood in front of a black curtain on the ground near the casket that faced mecca.
The crowd of thousands lined up directly in front of them, many holding their phones high in the air trying to capture video of the legend's coffin.
The service began with four recitations of "Allahu Akbar" or "God is Great," with silent prayers in between. They prayed that Ali find safe passage to the afterlife, and that his loved ones find a way to live without him.
Several speakers, including two Muslim women, described Ali's impact on their own lives and as a champion for civil rights and acceptance of the Islamic faith.
Jackson said Ali's passing "made us all feel a little more alone in the world" and detracted "from the sweetness of life itself."
"Ali inspired us. He filled us up. He gave us courage," he said. "And he taught us something about how to fight, not only inside the ring but outside as well."
The memorials come amid a fever of anti-Muslim political rhetoric and wave of assaults on U.S. mosques. Terrorist attacks carried out by Islamic extremists in Europe and California have caused many around the world to view the religion with fear or contempt.
Organizers of Ali's memorials say the events are not meant to be political.
Yet Muslim leaders and many faithful at the service say it represents a chance to demonstrate the beauty of the religion through the legacy of Ali, one of the most famous people on the planet.
"In this climate we live in today, with Islamophobia being on the rise and a lot of hate-mongering going on, I think it's amazing that someone of that caliber can unify the country and really show the world what Islam is about," said 25-year-old Abdul Rafay Basheer, who traveled from Chicago. "I think he was sort of the perfect person to do that."
A fellow Muslim who shares the boxing great's name arrived in Kentucky with no hotel reservation, just a belief that his 8,000-mile pilgrimage was important to say goodbye to a person considered a hero of his faith.
Mohammad Ali met the boxer in the early 1970s and they struck up a friendship based on their shared name. The Champ visited his home in 1978 and always joked he was his twin brother, he said. He stood weeping at the funeral, a green Bangladeshi flag draped over his shoulder, holding snapshots he took of the boxer during his visit, one standing with his family, another of him sprawled on a bed in his home.
Attending was so important to him, he delayed a scheduled open-heart surgery so he could travel around the world for the service.
Mustafa Abdush-Shakur leaned on his cane as he limped into the arena. He came 800 miles from Connecticut despite a recent knee replacement that makes it excruciating to walk.
"This is a physical pain," he said. "But had I not been able to come and pray for my brother, it would have caused me a spiritual pain and that would have been much deeper."
He believes Ali made the world more accommodating to Muslims.
"He never backed off from his religion he never denied who he was," he said. "He had an ability and a capacity to reach into places and to people who the average person wasn't able to reach."
AP religion reporter Rachel Zoll contributed to this report from New York. Reporters Jeff Karoub contributed from Detroit