Musannaf Ibn Abi Shayba 27:286

Ibn ‘Ulayyah narrated to us, from Ayyub, from ‘Ikrimah, who said: Ibn ‘Abbas said regarding Abu Bakr: As for what the Messenger of Allah (may Allah bless him and grant him peace) said: "If I were to take a *khalil* (intimate friend) from this nation, I would have taken him."