Musnad Ahmad 31:839

Mu'awiyah narrated to us, Abu Ishaq narrated to us, from al-Awza'i, al-Zuhri narrated to us, from 'Ata', from Abu Sa'id al-Khudri, who said: A man asked the Messenger of Allah, peace and blessings of Allah be upon him: "Which of the people is the best?" He then mentioned the meaning of the hadith of Shu'ayb.