Musnad Ahmad 32:1803

Husayn narrated to us, Jarir ibn Hazim narrated to us, from Muhammad ibn Sirin, from Anas ibn Malik, who said: The people were alarmed, so the Messenger of Allah (peace and blessings of Allah be upon him) mounted a horse belonging to Abu Talhah that was slow. Then he went out riding it alone, and the people rode out riding behind him. He said: "Do not be alarmed; it is indeed a sea." He said: By Allah, it was never outrun after that day.