Volume 1 · Book 12 · Hadith 710
Narrated Anas bin Malik: The Prophet, Abu Bakr and 'Umar used to start the prayer with "Al-hamdu lil-lahi Rabbil-'ala-min (All praises are for Allah the Lord of the Worlds)."
— Sahih Bukhari, Volume 1, Book 12: Characteristics of Prayer, Hadith #710