Sunan an-Nasa'i #3058 · The Book of Hajj

"The Messenger of Allah said to the people when they moved on the evening of Arafat and the morning of Jam' (assembly at Al-Muzdalifah): 'You must have tranquility.' He was reining in his camel, and when he entered Mina, he came down to Muhassir and said: 'You have to pick up pebbles the size of date stones of fingertips with which to stone the Jamrat.' And he (Al-Fadl) said: 'And the Prophet gestured with his hand like a man throwing a pebble