Musannaf Ibn Abi Shayba 22:208

Muhammad ibn Bishr narrated to us, he said: Muhammad ibn ‘Amr narrated to us, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The Quran was revealed in seven ahruf (modes/dialects): ‘Aliman Hakiman (All-Knowing, All-Wise), Ghafuran Rahiman (Oft-Forgiving, Most Merciful)."