Musnad Ahmad 32:2133

Bahz narrated to us, and 'Affan narrated to us, they said: Hammam narrated to us, Qatadah narrated to us, from Anas: "That the Messenger of Allah (ﷺ), and Abu Bakr, and 'Umar, and 'Uthman, used to begin the recitation after the Takbir with {Al-hamdu lillahi rabbil-'alamin} [Praise be to Allah, Lord of the worlds] in the prayer." 'Affan said: Meaning in the prayer after the Takbir.