The Prophet (ﷺ) used to say in his bowing and prostrations, "Subhanaka l-lahumma Rabbana wa bihamdika; Allahumma ghfir li.' (Exalted Are you O Allah our Lord, and by Your praise . O Allah! Forgive me).
Sahih al-Bukhari Book 10, Hadith 189
← Previous Hadith Once the Prophet (ﷺ) entered the mosque, a man came in, offered the prayer and greeted the Prophet. The Prophet returned his greeting and said to him, "Go back and pray again for you have not prayed." The man offered the prayer again, came back and greeted the Prophet. He said to him thrice, "Go back and pray again for you have not prayed." The man said, "By Him Who has sent you with the truth! I do not know a better way of praying. Kindly teach Me how to pray." He said, "When you stand for the prayer, say Takbir and then recite from the Qur'an what you know and then bow with calmness till you feel at ease, then rise from bowing till you stand straight. Afterwards prostrate calmly till you feel at ease and then raise (your head) and sit with Calmness till you feel at ease and then prostrate with calmness till you feel at ease in prostration and do the same in the whole of your prayer."

Sahih al-Bukhari Book 10, Hadith 188 Next Hadith → When the Prophet (ﷺ) said, "Sami`a l-lahu liman hamidah," (Allah heard those who sent praises to Him), he would say, "Rabbana wa laka l-hamd." On bowing and raising his head from it the Prophet (ﷺ) used to say Takbir. He also used to say Takbir on rising after the two prostrations. (See Hadith No. 656).

Sahih al-Bukhari Book 10, Hadith 190