From Sahih Bukhari (Hadith 690):
Narrated Al-Bara:(and he was not a liar) When Allah's Messenger (ﷺ) said, "Sami`a l-lahu liman hamidah" none of us bent his back (for prostration) till the Prophet (ﷺ) prostrated and then we would prostrate after him
Reference: Bukhari 690