Musannaf Ibn Abi Shayba 22:316

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