Sahih al-Bukhari 747
Sahih al-Bukhari · Book 10: Call to Prayers (Adhaan) · To cast a look at the Imam during As-Salat (the prayer)
Narrated Al-Bara:
حَدَّثَنَا حَجَّاجٌ ، حَدَّثَنَا شُعْبَةُ ، قَالَ أَنْبَأَنَا أَبُو إِسْحَاقَ ، قَالَ سَمِعْتُ عَبْدَ اللَّهِ بْنَ يَزِيدَ، يَخْطُبُ قَالَ حَدَّثَنَا الْبَرَاءُ ، وَكَانَ، غَيْرَ كَذُوبٍ أَنَّهُمْ كَانُوا إِذَا صَلَّوْا مَعَ النَّبِيِّ صلى الله عليه وسلم فَرَفَعَ رَأْسَهُ مِنَ الرُّكُوعِ قَامُوا قِيَامًا حَتَّى يَرَوْنَهُ قَدْ سَجَدَ.
(And Al-Bara was not a liar) Whenever we offered prayer with the Prophet (ﷺ) and he raised his head from the bowing, we used to remain standing till we saw him prostrating .