It is narrated from Sayyiduna Ka'b bin Ujrah (may Allah be pleased with him) that he said: The Messenger of Allah (peace and blessings be upon him) said: "The mu'aqqibat, whose sayer is never disappointed: glorifying Allah 33 times after every prayer, praising Him 33 times, and declaring His greatness 34 times."
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16310