Musnad Ahmad 26:586

'Abd al-Rahman narrated to us, Sufyan narrated to us, from Abu Ishaq, from Abu al-Ahwas, from 'Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "If I were to take a close friend (khalil), I would have taken the son of Abu Quhafa as a close friend."