Yahya bin Hind (may Allah have mercy on him) narrates from his father, Sayyiduna Harmalah bin Amr (may Allah be pleased with him), who said: I saw the Messenger of Allah (peace and blessings be upon him) at Arafah, and my uncle had me riding behind him. I looked at the Messenger of Allah (peace and blessings be upon him) and he ((peace and blessings be upon him)) was placing one of his fingers upon the other. He said: I asked: What is he saying? He (my uncle) said: He is saying: "Throw pebbles the size of a chickpea."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3461