Musannaf Ibn Abi Shayba 34:293

Malik narrated to us, he said: Sahl ibn Shu'ayb narrated to me, he said: Firas ibn Yahya narrated to me, he said: I obtained in the prison of al-Hajjaj a paper dotted with grammar, and it was the first dotting I had seen. So I brought it to al-Sha'bi and showed it to him. He said: "Read it, but do not dot it with your hand."