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: "If I were to take anyone as a khalil, I would take Abu Bakr; but your companion is the khalil of Allah."
"And the Qur'an has been revealed in seven modes (ahruf), and every verse of it has an outward and an inward (meaning)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10071