Musnad Ahmad 27:935

Hassan narrated to us, Zuhair narrated to us, Yazid ibn Abi Ziyad narrated to us, from Abd al-Rahman ibn Abi Layla, from Abdullah ibn Umar, who said: I was in a detachment of the detachments of the Messenger of Allah (peace and blessings of Allah be upon him), and the people retreated in a retreat, and I was among those who retreated. We said: "What shall we do? We have fled from the battle, and we have returned with wrath." Then we said: "If we enter Medina and spend the night there..." Then we said: "If we present ourselves to the Messenger of Allah (peace and blessings of Allah be upon him), if there is a repentance for us, otherwise we will go away." So we came to him before the morning prayer. He came out and said: "Who are the people?" We said: "We are the ones who fled." He said: "No, rather you are the ones who return (to the fight). I am your group, and I am the group of the Muslims." He said: So we came to him until we kissed his hand.