Chapter 5: Holding the arms out from one's side when bowing - كتاب التطبيق
أَخْبَرَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ، عَنِ ابْنِ عُلَيَّةَ، عَنْ عَطَاءِ بْنِ السَّائِبِ، عَنْ سَالِمٍ الْبَرَّادِ، قَالَ قَالَ أَبُو مَسْعُودٍ أَلاَ أُرِيكُمْ كَيْفَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي قُلْنَا بَلَى . فَقَامَ فَكَبَّرَ فَلَمَّا رَكَعَ جَافَى بَيْنَ إِبْطَيْهِ حَتَّى لَمَّا اسْتَقَرَّ كُلُّ شَىْءٍ مِنْهُ رَفَعَ رَأْسَهُ فَصَلَّى أَرْبَعَ رَكَعَاتٍ هَكَذَا وَقَالَ هَكَذَا رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يُصَلِّي .
It was narrated that Salim Al- Barrad said:
"Abu Mus'ad said: 'Shall I not show you how the Messenger of Allah (ﷺ) prayed?' We said: 'Yes.' So he stood up and said the takbir, and when he bowed, he held his arms out from his sides until, when every part of him settled, he raised his head. He prayed four rak'ahs like that, and said: 'This is how I saw the Messenger of Allah (ﷺ) praying.'"