The whole prayer

Bowing

Rukūʿ — bowing

The back level, the hands on the knees, and one sentence repeated.

سُبْحَانَ رَبِّيَ الْعَظِيمِ

Subḥāna Rabbiyal-ʿAẓīm

How far above all fault is my Master, the Immense.

Why it is said here

The body says what the words say. You bend before the Immense, and while bent you name Him immense — three times or more. The Prophet ﷺ said: 'As for the bowing, magnify your Lord in it.' It is the posture of someone who has heard an order and is not going to argue.