Narrated Ubayy bin Ka'b:
"The Messenger of Allah (ﷺ) met Jibra'il and said: 'O Jibra'il! I have been sent to an illiterate nation among whom are the elderly woman, the old man, the boy and the girl, and the man who cannot read a book at all.' He said: 'O Muhammad! Indeed the Qur'an was revealed in seven modes.'" (FR)
English reference (FR): Vol. 5, Book 43, Hadith 2944 (FR)
Arabic reference (FR): Book 46, Hadith 3196 (FR)