Riyad as-Salihin 15:13

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]