Iranians are participating in the event, which they boycotted past year due to a row between with Saudis on pilgrimage regulations.
From dawn until dusk, the massive crowd of people will be gathered here in Mount Arafat to spend the day in supplication and contemplation.
In his sermon, the holy Prophet called on the faithful to repay their debts, beware of Satan, perform five-time daily prayers, fast during the holy month of Ramadan and give charity.
Haj, the largest annual worldwide gathering, is the Muslim pilgrimage to Makkah, which began on Wednesday.
Pictures also show millions of pilgrims sleeping in the streets as they continue their journey to Muzdalifah - an open level area near Mecca.
Despite closing the border with Qatar on 5 June as part of the Gulf countries' economic and diplomatic offensive against the gas-rich emirate, Saudi Arabia has allowed 1,340 Qataris to enter the country for the Hajj.
"I'm so happy to be a part of it this year", said 43-year-old Nigerian Mohammed Said, in the seamless two-piece white garment or "ihram" worn by male pilgrims.
Health officials said they are also prepared to deal with any injuries or accidents and have more than 100 ambulances deployed across the hajj sites.
An elderly Syrian pilgrim sitting on the hilltop shouted out, "Oh God, take revenge on the oppressors".
The Eid al-Adha, or feast of the sacrifice, starts on Friday, when pilgrims begin three days of casting stones at walls in a symbolic renunciation of the devil. On YouTube, they telecast live hajj and now, Google, iTunes and other sites have come out with hajj apps to help pilgrims better understand and perform the hajj rituals.
The Kaaba represents the metaphorical house of God and the oneness of God in Islam.
Men shave their heads or cut their hair, while women cut the ends of their hair, as a sign of humility and purity.
Eid Al Adha is celebrated by the millions of Muslims in remembrance of Prophet Ibrahim who made his mind for sacrificing his son.
According to him, Arafat day is significant to all Muslims, adding that it is the day Allah answers prayers of His servants.