Language:
كتاب الصلاة
8  
Prayers (Salat)
(40)
Chapter: Preaching of the Imam to the people regarding the proper offering of As-Salat (the prayers) and the mention of the Qiblah (Kabah at Makkah)
(40)
باب عِظَةِ الإِمَامِ النَّاسَ فِي إِتْمَامِ الصَّلاَةِ، وَذِكْرِ الْقِبْلَةِ
Sahih al-Bukhari 418

Narrated Abu Huraira:

Allah's Messenger (ﷺ) 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 ‏"‏‏.‏
Reference : Sahih al-Bukhari 418
In-book reference : Book 8, Hadith 68
USC-MSA web (English) reference : Vol. 1, Book 8, Hadith 410
  (deprecated numbering scheme)