Assalamualaikum Warahamathulahi Wabarakatuhu
Stoning shaitan is a important part of HAJJ (Major Pilgrimage). This ritual is called as JAMARAT. The believers (Muslims) as one part of Hajj, they throw 7 stones at three shaitan (stones) placed in Mina. This ritual came into being at the time of Ibrahim (Alaihiwassalam). When he was on his way to sacrifice his dearest son Ismail, three shaitans appeared on his way and tried to deviate his mind. And that’s when Jibraeel (Alaihiwassalam), said Ibrahim (Alaihiwassalam) to throw 7 stones on each shaitan that came on his way. And that’s the three shaitan which is placed as stone in Mina.
My Lord, grant me [a child] from among the righteous. So We gave him good tidings of a forbearing boy. And when he reached with him [the age of] exertion, he said, “O my son, indeed I have seen in a dream that I [must] sacrifice you, so see what you think.” He said, “O my father, do as you are commanded. You will find me, if Allah wills, of the steadfast.” [ Surah As-Saffat, Ayath-100-102]
And due to which, all believers follow this ritual. And the stones (size of pebble) are to be collected from Musdhalifa on 10th day of Dhu-Al-Hajjah. And the pilgrims have to spend the 11th, 12th and 13th night at Mina and stone the Jamarat after the sun set. The name of the Jamarats are Jamrat Al-Sughra (smallest of three), Jamrat Al-Wusta (the middle one) and Jamrat Al-Aqabah (largest one).
And reward for Stoning Shaitan is mentioned here. It has been narrated from Abi ‘Abdillah [Imam Ja’far Ibn Muhammad as-Sadiq] in regards to the stoning of the Shaitan that he said, “For every stone that a pilgrim throws, a major sin, which would have led to his destruction, is averted from him.” [ Biharul Anwar, Volume-96, Page#273]
And after this, Qurbani is given. It also arises from Prophet Ibrahim (Alaihiwassalam), where he cuts the head of his son Ismail and ALLAH the most-merciful transforms him into a goat. From, where the Qurbani also became a part of HAJJ. And this is the purpose of stoning the shaitan during Hajj.