Musannaf Ibn Abi Shayba 3:6177

Waki’ narrated to us, he said: Ali bin Mubarak narrated to us, from Abu Hakimah al-‘Abdi, who said: We used to write the Mushafs (copies of the Quran) in Kufa. Ali would pass by us and stand and look, and our handwriting would please him. He would say: "Thus, illuminate what Allah has illuminated."