كتاب الأذكار
16
The Book of the Remembrance of Allah
Ka'b bin 'Ujrah (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) said, "There are some words, the reciters of which will never be disappointed. These are: Tasbih [saying 'Subhan-Allah' (Allah is free from imperfection)], thirty-three times, Tahmid [saying 'Al-hamdu lillah' (praise be to Allah)] thirty-three times and Takbir [saying 'Allahu Akbar' (Allah is Greatest)] thirty-four times; and these should be recited after the conclusion of every prescribed prayer."

[Muslim]

وعن كعب بن عجرة رضي الله عنه عن رسول الله صلى الله عليه وسلم قال‏:‏ ‏ "‏معقبات لا يخيب قائلهن -أو فاعلهن- دبر كل صلاة مكتوبة‏:‏ ثلاثًا وثلاثين تسبيحة وثلاثًا وثلاثين تحميدة، وأربعًا وثلاثين تكبيرة‏"‏ ‏(‏‏(‏رواه مسلم‏)‏‏)‏‏.‏
Sunnah.com reference : Book 16, Hadith 13
Arabic/English book reference : Book 16, Hadith 1420