Sahih al-Bukhari 800
Sahih al-Bukhari · Book 10: Call to Prayers (Adhaan) · To stand Straight with calmness on raising the head from bowing
Narrated Thabit:
حَدَّثَنَا أَبُو الْوَلِيدِ ، قَالَ حَدَّثَنَا شُعْبَةُ ، عَنْ ثَابِتٍ ، قَالَ كَانَ أَنَسٌ يَنْعَتُ لَنَا صَلاَةَ النَّبِيِّ صلى الله عليه وسلم فَكَانَ يُصَلِّي وَإِذَا رَفَعَ رَأْسَهُ مِنَ الرُّكُوعِ قَامَ حَتَّى نَقُولَ قَدْ نَسِيَ.
Anas used to demonstrate to us the prayer of the Prophet (ﷺ) and while demonstrating, he used to raise his head from bowing and stand so long that we would say that he had forgotten (the prostration).