Musannaf Ibn Abi Shayba 3:6347

Abu Bakr narrated to us, he said: Abu al-Ahwas narrated to us, from Mughira, from Ibrahim, from Alqama, who said: I recited before Abdullah, and he said: "Recite slowly (tartil), may my father and mother be sacrificed for you, for it is the adornment of the Quran."