On the days of Mina, pilgrims throw pebbles at three stone pillars (the Jamarat), a rite most Muslims associate with the tradition of Ibrahim being tempted by Shaytan to abandon Allah's command and driving him away by pelting him with stones at these very locations — a story reported in early Islamic sources though not detailed in the Quran itself.
More fundamentally, the Prophet ﷺ explained the purpose behind this rite and others like it in a hadith narrated by Aisha: "Circumambulation of the House, the going between Safa and Marwah, and the stoning of the Jamarat were only established for the remembrance of Allah" (Sunan Abi Dawud 1888). In other words, the outward physical act is secondary to its inner purpose — turning the heart toward Allah through deliberate, remembered obedience, even in an act that carries no logical utility on its own. Stoning is performed on the 10th of Dhul-Hijjah (Jamrat al-Aqabah only) and on the 11th–13th (all three, in order, starting with the smallest), and it is one of the wajibaat of Hajj rather than a pillar.