Musannaf Ibn Abi Shayba 3:4571

Abu Bakr narrated to us, he said: Abd al-Salam ibn Harb narrated to us, from Layth, from Abd al-Rahman ibn al-Aswad, from his father, that Abdullah ibn Mas’ud, when he finished the recitation, would say "Allahu Akbar" (takbir), then he would perform the Qunut. When he finished the Qunut, he would say "Allahu Akbar" (takbir), then he would bow (ruku).