See Muslim Pilgrims Flocking to Mecca for the Hajj

Muslim pilgrims circle the Kaaba, the cubic building at the Grand Mosque in the Muslim holy city of Mecca, Saudi Arabia, on Sept. 15, 2015.

Mosa'ab Elshamy—AP

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Muslim Pilgrims pray during Friday afternoon prayers outside the Grand Mosque in the holy city of Mecca, on Sep. 18, 2015.

Mosa'ab Elshamy—AP

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A Muslim Pilgrim prays outside the Grand Mosque in the holy city of Mecca, on Sept. 20, 2015.

Mosa'ab Elshamy—AP

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Water is sprayed over Muslim pilgrims to cool them down during the afternoon heat as they walk outside the Grand Mosque in the holy city of Mecca, on Sept. 15, 2015.

Mosa'ab Elshamy—AP

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Thousands of tents are prepared to host millions of Muslim pilgrims during the annual pilgrimage, known as the Hajj, in Mina, on the outskirts of the holy city of Mecca, on Sept. 19, 2015.

Mosa'ab Elshamy—AP

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A Saudi security officers monitors live feed screens showing Muslim pilgrims in the holy city of Mecca, along with highways and high density areas, a few days before the annual pilgrimage, known as the hajj, in Mecca, on Sept. 19, 2015.

Mosa'ab Elshamy—AP

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Saudi security officers monitor live feed screens showing Muslim pilgrims in the holy city of Mecca, along with highways and high density areas, a few days before the annual pilgrimage, known as the hajj, in Mecca, on Sept. 19, 2015.

Mosa'ab Elshamy—AP

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Muslim pilgrims pray at the Kaaba, the cubic building at the Grand Mosque in the Muslim holy city of Mecca, on Sept. 20, 2015.

Mosa'ab Elshamy—AP

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Muslim pilgrims rest inside the Grand Mosque in the holy city of Mecca, on Sept. 20, 2015.

Mosa'ab Elshamy—AP

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Muslim pilgrims pray atop the Noor Mountain outside the Hiraa cave, where Prophet Muhammad received his first revelation from God to preach Islam, on the outskirts of Mecca, on Sept. 18, 2015.

Mosa'ab Elshamy—AP

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By TIME Photo

September 21, 2015 7:53 PM EDT