Musnad Abu Ya'la al-Mawsili 153:182

Harun ibn Ma'ruf narrated to us, Sufyan narrated to us, from Yazid ibn Abi Ziyad, from Abd al-Rahman ibn Abi Layla, from Ibn Umar, who said: The Messenger of Allah (ﷺ) sent us in a military expedition, and we retreated a retreat. Then we entered Medina and hid ourselves. He said: We said, "We are ruined, O Messenger of Allah! We are the ones who fled." He said: "No, rather you are the ones who return to the fight (al-akkarun), and I am your group (fi'ah)."