With the chain of Ahmad, it is reported from Sayyiduna Hudhayfah (may Allah be pleased with him): The Prophet (peace and blessings be upon him) said: "I met Jibril at the place of 'Ahjar al-Mira', and I said: 'O Jibril! I have been sent to an unlettered nation, who do not know how to read and write; among them are men, women, boys, girls and elderly people who have never read any writing.' Jibril said: 'Indeed, the Qur'an has been revealed in seven ahruf.'"
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب التفسير / 11566