Musnad Ahmad 27:1302

Khalaf ibn al-Walid narrated to us, Khalid—meaning al-Tahhan—narrated to us, from Yazid ibn Abi Ziyad, from Abd al-Rahman ibn Abi Layla, from Ibn Umar, who said: We met the enemy, and the Muslims retreated in a retreat, and I was among those who retreated. We entered Medina. He said: So we presented ourselves to the Messenger of Allah, peace and blessings of Allah be upon him, when he came out for prayer. We said: "O Messenger of Allah, we are the ones who fled." He said: "Rather, you are the ones who return to the fight; I am your support group."