Riyad us Saliheen: Hadith 1458

The Messenger of Allah (ﷺ) said to me and to Fatimah (May Allah be pleased with her) (Ali's wife and the Prophet's daughter), "When you go to bed, recite: Takbir (Allahu Akbar) thirty-three times and Tasbih (Subhan-Allah) thirty-three times and Tahmid (Al-hamdu lillah) thirty-three times."

Another narration is: The Messenger of Allah (ﷺ) said, "Recite Tasbih thirty-four times."

Another narration is: The Messenger of Allah (ﷺ) said, "Recite Takbir thirty-four times."

[Al-Bukhari and Muslim].