Musannaf Ibn Abi Shayba 8:1478

Abu Bakr narrated to us, he said: Yahya bin Salim al-Ta’ifi narrated to us, from Abdullah bin Uthman, he said: I heard Mujahid and Sa’id bin Jubayr saying: We used to see Abdullah [bin Umar] when he threw the Jamrah, he would raise his hands until they were level with his head, and the whiteness of his armpits could be seen. And his pebbles were like the size of a hazelnut.