Musnad Ahmad 32:195

Yahya narrated to us, Hisham narrated to us, Qatadah narrated to us, from Anas ibn Malik: "That the Messenger of Allah (may Allah bless him and grant him peace), and Abu Bakr, and Umar, and Uthman, used to begin the recitation with: {All praise is due to Allah, Lord of the worlds} [Al-Fatihah: 2]."