Sahih Muslim Book - 4, Hadith - 1064

حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ الرَّحْمَنِ بْنِ سَهْمٍ الأَنْطَاكِىُّ حَدَّثَنَا إِبْرَاهِيمُ بْنُ مُحَمَّدٍ أَبُو إِسْحَاقَ الْفَزَارِىُّ عَنْ أَبِى إِسْحَاقَ الشَّيْبَانِىِّ عَنْ مُحَارِبِ بْنِ دِثَارٍ قَالَ سَمِعْتُ عَبْدَ اللَّهِ بْنَ يَزِيدَ يَقُولُ عَلَى الْمِنْبَرِ حَدَّثَنَا الْبَرَاءُ أَنَّهُمْ كَانُوا يُصَلُّونَ مَعَ رَسُولِ اللَّهِ -صلى الله عليه وسلم- فَإِذَا رَكَعَ رَكَعُوا وَإِذَا رَفَعَ رَأْسَهُ مِنَ الرُّكُوعِ فَقَالَ « سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ ». لَمْ نَزَلْ قِيَامًا حَتَّى نَرَاهُ قَدْ وَضَعَ وَجْهَهُ فِى الأَرْضِ ثُمَّ نَتَّبِعُهُ.

It was narrated that Muharib bin Dithar said: "I heard 'Abdullah bin Yazid saying on the Minbar: 'Al-Bara' told me that they used to offer prayers with the Messenger of Allah (s.a.w). When he bowed, they bowed, and when he raised his head from bowing and said: "Sami'a Allahu liman hamidah," we would remain standing until we saw that he had placed his forehead on the ground, then we would follow him."