Musnad Ahmad 33:670

'Abd al-Samad and 'Affan narrated to us, they said: Hammad narrated to us. 'Affan said in his narration: Abu al-Zubayr informed us. And 'Abd al-Samad said in his narration: Abu al-Zubayr narrated to us, from Jabir ibn 'Abd Allah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "I saw as if I were in a fortified coat of mail, and I saw slaughtered cows. I interpreted the fortified coat of mail as Medina, and the cows as a group of people, and Allah is better." He said: So he said to his companions: "If we were to stay in Medina, then if they enter upon us within it, we will fight them." They said: "O Messenger of Allah, by Allah, they did not enter upon us within it during the Jahiliyyah, so how would they enter upon us within it in Islam?" 'Affan said in his narration: So he said: "Your affair then." He said: So he put on his armor. He said: Then the Ansar said: "We have turned back the opinion of the Messenger of Allah (peace and blessings of Allah be upon him)." So they came and said: "O Prophet of Allah, your affair then." He said: "It is not for a prophet, when he has put on his armor, to take it off until he fights."