Musnad Ahmad 32:801

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, and Hajjaj said: Shu'bah narrated to me, I heard Qatadah narrating from Anas ibn Malik, who said: There was a panic in Medina, so the Messenger of Allah (peace and blessings of Allah be upon him) borrowed a horse of ours that was called Mandub. The Messenger of Allah (peace and blessings of Allah be upon him) said: "We did not see any panic, and we found him to be a sea [i.e., very swift and vast in movement]." Hajjaj said: "Meaning the horse."