Musnad Ahmad 33:107

Waki' narrated to us, Sufyan narrated to us, from Abu al-Zubayr, from Jabir, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Let my nation take their rites [of Hajj], and throw [at the Jamarat] with the likes of the pebbles of al-khadhf (small pebbles thrown by placing them between two fingers)."