Muhammad bin Ibrahim al-Taymi (may Allah have mercy on him) said that a man from his people said: I heard the Prophet (peace and blessings be upon him) teaching the people their rites, and he was saying: "Throw small pebbles like those used for khadhf (flicking)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9537