From Sahih Muslim (Hadith 1349):
Ka'b b. 'Ujra reported Allah's Messenger (ﷺ) as saying:There are certain ejaculations, the repeaters of which or the performers of which after every prescribed 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
Reference: Muslim 1349