Musnad Ahmad 1793

Abu Ma"bad said: I heard Ibn ‘Abbas narrate that al-Fadl said: The Messenger of Allah (ﷺ) said on the evening of "Arafah and the morning of Muzdalifah to the people as they were moving on: "Keep 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."