Musnad Ahmad 1820

It was narrated from ‘Abdullah bin ‘Abbas, from al-Fadl bin ‘Abbas, from the Messenger of Allah (ﷺ) that he said on the evening of "Arafah and the morning of Muzdalifah to the people when they moved on: "You should be calm.” And he was reining in his she-camel until he entered Mina when he came down from Muhassir. He said: "Pick up small pebbles (the size of broad beans) with which to stone the Jamrah." And the Prophet (ﷺ) indicated with his hand how a person should throw (the pebbles).