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).
حَدَّثَنَا حَفْصُ بْنُ عُمَرَ، حَدَّثَنَا شُعْبَةُ، عَنْ أَبِي إِسْحَاقَ، قَالَ سَمِعْتُ عَبْدَ اللَّهِ بْنَ يَزِيدَ الْخَطْمِيَّ، يَخْطُبُ النَّاسَ قَالَ حَدَّثَنَا الْبَرَاءُ، - وَهُوَ غَيْرُ كَذُوبٍ - أَنَّهُمْ كَانُوا إِذَا رَفَعُوا رُءُوسَهُمْ مِنَ الرُّكُوعِ مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم قَامُوا قِيَامًا فَإِذَا رَأَوْهُ قَدْ سَجَدَ سَجَدُوا .
AbuDaud
Prayer (Kitab Al-Salat) • Hadith 620