Musnad Ahmad 26:203

Abu al-Walid narrated to us, Abu 'Awanah narrated to us, from 'Abd al-Malik, from Khalid ibn Rib'i al-Asadi, who said: I heard Ibn Mas'ud saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Indeed, your companion is the Khalil (intimate friend) of Allah, the Almighty and Majestic."