Musannaf Ibn Abi Shayba 3:460

Abu Bakr narrated to us, he said: Hafs narrated to us, from ‘Amr, from al-Hasan, who said: The Messenger of Allah (may Allah bless him and grant him peace) had three silences: when he began the takbir until he recited the Hamd (al-Fatiha), and when he finished the Hamd until he recited the surah, and when he finished the surah until he bowed.