Sunan Abi Dawud Book 2, Hadith 230
Al-Bara who is not a liar said; when they (the companions) raised their heads from bowing along with the Messenger of Allah (ﷺ), they would stand up, and when they saw him that he went down in prostration, they would prostrate (following the prophet).
The Prophet (ﷺ) said: Do not try to outstrip me in bowing and prostrating because however earlier I bow you will join me when I raise (my head from bowing); I have become bulky.
Al-Bara b.‘Azib said ; we used to pray along with the prophet (ﷺ); none of us bowed his back until he saw that the prophet (ﷺ) bowed (his back).