Musnad Ahmad 32:867

Muhammad ibn Ja'far narrated to us, Shu'bah and Hajjaj narrated to us, he said: Shu'bah narrated to me, he said: I heard Qatadah narrating from Anas ibn Malik, who said: "I prayed with the Messenger of Allah (may Allah bless him and grant him peace), and Abu Bakr, and Umar, and Uthman, and I did not hear any one of them reciting: 'In the name of Allah, the Entirely Merciful, the Especially Merciful' [Al-Fatihah: 1]." Hajjaj said: Shu'bah said: Qatadah said: I asked Anas ibn Malik: "With what did the Messenger of Allah (may Allah bless him and grant him peace) begin the recitation?" He said: "You are asking me about something that no one has asked me about."