Musnad Ahmad 26:33

Sufyan narrated to us, from al-A’mash, from ‘Abdullah ibn Murrah, from Abu al-Ahwas, from ‘Abdullah, from the Prophet (peace and blessings of Allah be upon him): "I disassociate myself from every intimate friend (khalil) because of his intimacy. And if I were to take an intimate friend, I would have taken Abu Bakr as an intimate friend. But your companion is the intimate friend of Allah, the Almighty and Majestic."