Sahih al-Bukhari, Hadith 418 ⓘ
Narrated Abu Huraira: Allah's Messenger said, "Do you consider or see that my face is towards the Qibla? By Allah, neither your submissiveness nor your bowing is hidden from me, surely I see you from my back."
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، قَالَ أَخْبَرَنَا مَالِكٌ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " هَلْ تَرَوْنَ قِبْلَتِي هَا هُنَا فَوَاللَّهِ مَا يَخْفَى عَلَىَّ خُشُوعُكُمْ وَلاَ رُكُوعُكُمْ، إِنِّي لأَرَاكُمْ مِنْ وَرَاءِ ظَهْرِي " .
also referenced under: Book 8, Hadith 68 (In-Book) & Volume 1, Book 8, Hadith 410 (USC-MSA)