Musnad Ahmad 26:328

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Abu Ishaq, from Abu al-Ahwas, from Ibn Mas'ud, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "If I were to take anyone as a *khalil* (intimate friend), I would have taken the son of Abu Quhafa as a *khalil*."