Musnad Ahmad 266:2

'Abd al-Rahman ibn Mahdi narrated to us, from Sufyan, from Abu al-Zinad, from Abu Salamah, from Abu Usayd al-Sa'idi, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The best of the Ansar are the Banu al-Najjar, then the Banu 'Abd al-Ashhal, then the Banu al-Harith ibn al-Khazraj, then the Banu Sa'idah." Then he said: "And in all of the Ansar there is good."