Musnad Ahmad 1034:157

'Affan narrated to us, Hammad—meaning Ibn Salamah—narrated to us, from 'Asim, from Zirr, from Hudhayfah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "I met Jibril (peace be upon him) at the stones of Al-Mira'. He said: 'O Jibril, I have been sent to an unlettered nation: the man and the woman, the boy and the girl, and the elderly person who has never read a book at all.' He said: 'Indeed, the Qur'an was revealed in seven ahruf (modes/dialects).'"