Sahih al-Bukhari, Volume 1, Book 12, Hadith 765 (USC-MSA) ⓘ
Narrated Thabit: Anas used to demonstrate to us the prayer of the Prophet 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).
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.
also referenced under: Book 10, Hadith 195 (In-Book) & Hadith 800 (DarusSalam)