Musannaf Ibn Abi Shayba 22:201

Ishaq al-Azraq narrated to us from al-A’mash, who said: Ibrahim said to me, "Ibrahim al-Taymi wants you to teach him the recitation of Abdullah." I said, "I cannot." He said, "Yes, you can." He said, "For he has indeed wanted that." He said: So when I saw him, I said, "Shall this be in your presence, so we may discuss the letters of Abdullah?" He said, "This is not sufficient." I said, "And what do you dislike about this?" He said, "I dislike that I should say, 'It is not like this,' or that I should say, 'There is a *waw* in it,' when there is no *waw* in it."