Sahih Al Bukhari Hadith Number 743

Narrated Anas bin Malik: The Prophet, Abu Bakr and `Umar used to start the prayer with “Al hamdu li l-lahi Rabbi l-`alamin (All praise is but to Allah, Lord of the Worlds).

10  Call to Prayers (Adhaan)
Hadith number 743
Volume no 1
Chapter: 89 (What to say after the Takbir)