Musannaf Ibn Abi Shayba 3:1767

Waki’ narrated to us, from Shu’bah, from Qatadah, from Anas, who said: I prayed behind the Prophet (peace and blessings of Allah be upon him), and Abu Bakr, and Umar, and Uthman, and they did not recite "Bismillah al-Rahman al-Rahim" aloud.