Musnad Ahmad 32:1840

Al-Ahwas ibn Jawwab narrated to us, Ammar ibn Ruzayq narrated to us, from al-A’mash, from Shu’bah, from Thabit, from Anas, who said: "I prayed with the Messenger of Allah, peace and blessings of Allah be upon him, and with Abu Bakr, and with Umar, and they did not recite 'In the name of Allah, the Most Gracious, the Most Merciful' aloud."