In unison, the crowd repeated "God is great" in Arabic during a prayer, marking the beginning of Eid al-Adha, a Muslim celebration.
"This is the Eid in regard to the holiday of the story of Abraham with his son Ishmael and his order from God to sacrifice his son," said Imam Jamal Diwan with the Islamic Center of Irvine.
According to the Quran, God spared Abraham's son and gave him a ram to sacrifice instead, which Abraham then prepared for a feast. That's what the event revolved around.
"These are days that Prophet Mohammed said are days of festivities and remembrance of God," said Imam Mohammed Faqih of the Islamic Institute of Orange County.
Usually, Eid prayer celebrations aren't on this scale. In the past, it would be up to mosques to organize their own individual events at much smaller venues, like a hall at the Anaheim Convention Center.
But this year for the first time ever, the three largest Islamic centers in Orange County teamed up to get the ball park. More than 20,000 people filed in, covered the baseball diamond, took off their shoes and bowed in prayer.
"Seeing the magnitude of the people from all over the world all over the county all over SoCal just come together to pray its phenomenal. It touches my heart," said Annan Aboul-Nasr of Anaheim.
The Eid prayer also marked the end of Hajj, the pilgrimage to Mecca each Muslim is to make at least once in their lifetime. But the celebration is far from over. Eid al-Adha continues through Sunday.