Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1242
Ka'b b. 'Ujra reported Allah's Messenger (may peace be upon him) as saying: There are certain ejaculations, the repeaters of which or the performers of which at the end of every prayer will never be caused disappointment:" Glory be to Allah" thirty-three times," Praise be to Allah" thirty-three times, and" Allah is most Great" thirty-four times.