It is narrated from Sayyiduna Ka'b bin Ujrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "The mu'aqqibat, whose sayer or doer is never disappointed: tasbih 33 times, tahmid 33 times, and takbir 34 times after every prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16313