Sahih Bukhari | Volume 8 | Hadith Number 673

Narrated by Abu Huraira
Allah's Apostle said, "(Following are) two words (sentences or utterances that are very easy for the tongue to say, and very heavy in the balance (of reward,) and the must beloved to the Gracious Almighty (And they are): Subhan Allah wa bi-hamdihi; Subhan Allahi-l-'Azim."