It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "This companion of yours is the Khalil (intimate friend) of Allah," meaning that he (peace and blessings be upon him) was referring to himself.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10500