Musnad Ahmad 218:1

Abu Mu’awiyah narrated to us, he said: Hilal ibn ‘Amir al-Muzani narrated to us, from his father, who said: I saw the Messenger of Allah (peace and blessings of Allah be upon him) addressing the people at Mina while on a mule, and upon him was a red cloak. He said: And a man from the people of Badr was in front of him, repeating what he said. He said: So I came until I inserted my hand between his foot and his sandal strap. He said: "And I began to marvel at its coolness."