Sunan an-Nasa'i 1349
سنن النسائي#1349SahihIt was narrated that Ka'b bin 'Ujrah said:"The Messenger of Allah (ﷺ) said: 'There are statements of remembrance following the prayer of which the one who says them will never be deprive of the reward: Glorifying Allah (SWT) thirty-three times following each prayer, and praising Him thirty-three times, and magnifying Him thirty-four times
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih Muslim
In-book reference: 13:171