Sahih Bukhari
Sahih Bukhari Volume 001, Book 012, Hadith Number 710.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 12. Charecteristics Of Prayer
Narated By 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)."