Musannaf Ibn Abi Shayba 3:86

Waki’ narrated to us, from Ziyad ibn Abi Muslim, who said: I heard Abu al-‘Aliyah being asked: "With what did the prophets begin the prayer?" He said: "With the declaration of oneness (Tawhid), the declaration of glorification (Tasbih), and the declaration of divinity (Tahlil)."