The Eid al-Adha, meaning the feast of sacrifice, commemorates Abraham's readiness to sacrifice his son in God's test of the patriarch's faith. At the last moment, God substituted a sheep for the son.
The story is shared by all the great monotheistic religions -Islam, Judaism and Christianity. Pilgrims flocked to the site at Mina's Jamarat Bridge to cast the first set of stones before the crowds arrived.
They must stand and stone three thick walls in a symbolic casting out of the devil and rejection of temptation.
The occasion is subject to strict security as it had witnessed deadly stampedes in the past, like in 2004 when 250 pilgrims were trampled to death.
In a message marking Tuesday's Eid al-Adha holiday, King Abdullah and Crown Prince Sultan of Saudi Arabia said: "We ask God to make this Eid one of peace and stability for Muslims and the whole world and unite Muslims in goodness and inspire them to do what is right."
This year's pilgrimage has been overshadowed by the collapse of a Makka hostel that killed 76 people on Thursday and warnings of a possible spread of bird flu due to the huge crowds.
An estimated 2.5 million pilgrims
are expected in Makka
Saudi Arabia has deployed a record 60,000-strong security force to control the huge crowds and avert attacks by Muslim fighters who oppose the US-allied Saudi royal family.
Pilgrims must perform the stoning ritual three times. Many will stay in Jamarat until Thursday, the end of the five-day Hajj, whose rules were laid out by the Prophet Mohammad 1400 years ago.
The Hajj is a journey every able-bodied Muslim is urged to complete at least once in his/her lifetime.
The government has reorganised access to the Jamarat area and promised to remove pilgrim squatters who camp there.
Symbol of equality
Pilgrims, male and female, complete the first stoning session and then go to Makka to circle the Kaaba, which symbolises the house of God, dressed in white robes meant to eradicate class and make all Muslims equal.
The state-appointed preacher at the Grand Mosque, Sheikh Abdulrahman al-Sudais, urged Muslims in his Eid sermon to remember their Muslim brothers in the Israeli-Palestinian conflict and in Iraq.
He also said the West was using the phenomenon of terrorism to scare people away from Islam. "Muslims are being described in insulting terms to distort the image of Islam and scare people away from it," he said.
The collapse of a Makka hostel
has cast a shadow on the Hajj
During Eid, Muslims slay livestock as a reminder of Abraham's willingness to sacrifice his son Ismail at God's command. Pilgrims buy special coupons from Hajj organisers that represent the slain animal.
Makka, a trading city that relies on the pilgrim traffic to sustain the local economy, comes alive as pilgrims flock to the Grand Mosque and circle the Kaaba and then queue at barbers for a haircut.The legitimacy of Saudi Arabia's ruling house rests in the eyes of many Muslims on its ability to host some 2.5 million Hajj pilgrims every year.