Musnad Ahmad 274:1

Abu al-Yaman narrated to us, he said: Shu'ayb informed us, from al-Zuhri, he said: 'Abdullah ibn Ka'b ibn Malik al-Ansari—and he is one of the three who were forgiven—informed me that some of the companions of the Prophet, peace and blessings of Allah be upon him, informed him that the Prophet, peace and blessings of Allah be upon him, went out one day with his head bound, and he said in his sermon: "To proceed: O assembly of the Muhajirun, you have become increasing in number, while the Ansar have not increased beyond the state they are in today. The Ansar are my inner circle (lit. my bag/receptacle) to which I have sought refuge. So, honor their noble ones, and overlook the faults of their wrongdoers."