Musnad Ahmad 941:41

Yahya ibn Sa'id narrated to us, Hisham narrated to us, my father narrated to me, he said: Usamah was asked about the pace of the Messenger of Allah (peace and blessings of Allah be upon him) during the Farewell Pilgrimage, and I was a witness. He said: "His pace was *al-'anaq* (a moderate, steady trot). And when he found an opening, he would *nass* (increase the pace), and *al-nass* is above *al-'anaq*, and I was riding behind him."