Musnad Abu Ya'la al-Mawsili 161:60

Muhammad ibn Abd al-Rahman ibn Sahm al-Antaki narrated to us, Muhammad ibn Kathir al-San'ani narrated to us, from Ma'mar, from al-Zuhri, from Kathir ibn al-Abbas, who said: My father, al-Abbas ibn Abd al-Muttalib, narrated to me, saying: I witnessed Hunayn with the Messenger of Allah, may Allah bless him and grant him peace. When the Muslims were defeated, the Messenger of Allah, may Allah bless him and grant him peace, was upon a mule that Farwah ibn Nufathah al-Judhami had gifted to him. The Messenger of Allah, may Allah bless him and grant him peace, began to urge it toward the faces of the disbelievers, while I was holding its bridle for fear that it might go too fast, and Abu Sufyan ibn al-Harith ibn Abd al-Muttalib was holding the stirrup of the Messenger of Allah, may Allah bless him and grant him peace. He said: The Messenger of Allah, may Allah bless him and grant him peace, said: "Call out to the Companions of the Samurah (the tree)." So I called out at the top of my voice: "O Companions of the Samurah!" And they called out to the Ansar: "O company of the Ansar!" Then the call was narrowed down to the Banu al-Harith ibn al-Khazraj, and they were the most patient in the face of death. They said: "Labbayk, Labbayk (at your service, at your service)!" By Allah, I did not liken their turning toward the Messenger of Allah, may Allah bless him and grant him peace, to anything except the turning of cows toward their calves. He said: So they advanced and fought a fierce battle. When the Messenger of Allah, may Allah bless him and grant him peace, saw that, he took a handful of pebbles and threw them at the faces of the people and said: "May the faces be disfigured." He said: By Allah, I continued to see their sharpness blunted and their affair in retreat until Allah defeated them.