Sayyiduna Ka'b bin Ujrah (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "The mu'aqqibat, whose sayer or doer is never disappointed: glorifying Allah 33 times, praising Him 33 times, and declaring His greatness 34 times after every prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16314