Sahih Muslim Book 35, Hadith Number 6511.
Chapter : The merit of pronouncing Tablil, Tasbib and supplication.
Abu Huraira reported Allah’s Messenger (may peace be upon him) as saying: Two are the expressions which are light on the tongue, but heavy in scale, dear to the Compassionate One: “Hallowed be Allah and praise is due to Him”; “Hallowed be Allah, the Great.”