"When we performed Salat behind Messenger of Allah, he would raise his head from bowing, and no man among us would bend his back until Messenger of Allah prostrated, then we prostrated."  

كُنَّا إِذَا صَلَّيْنَا خَلْفَ رَسُولِ اللَّهِ ﷺ فَرَفَعَ رَأْسَهُ مِنَ الرُّكُوعِ لَمْ يَحْنِ رَجُلٌ مِنَّا ظَهْرَهُ حَتَّى يَسْجُدَ رَسُولُ اللَّهِ ﷺ فَنَسْجُدَ قَالَ وَفِي الْبَابِ عَنْ أَنَسٍ وَمُعَاوِيَةَ وَابْنِ مَسْعَدَةَ صَاحِبِ الْجُيُوشِ وَأَبِي هُرَيْرَةَ