Musnad Ahmad 941:70

Waki’ narrated to us, ‘Umar ibn Dharr narrated to us, from Mujahid, from Usamah ibn Zayd: That the Prophet (peace and blessings of Allah be upon him) let him ride behind him from ‘Arafah. He said: The people said, "Our companion will inform us of what he did." Usamah said: "When he departed from ‘Arafah, he pulled the head of his mount until its head reached the middle of the saddle, or nearly reached it, gesturing to the people with his hand: 'Tranquility, tranquility, tranquility,' until he reached Jam’." Then he let al-Fadl ibn ‘Abbas ride behind him. He said: The people said, "Our companion will inform us of what the Messenger of Allah (peace and blessings of Allah be upon him) did." Al-Fadl said: "He continued to travel at a gentle pace, like his pace yesterday, until he reached the valley of Muhassir, where he urged it forward until the ground became level for him."