Sahih al-Bukhari 741
Sahih al-Bukhari · Book 10: Call to Prayers (Adhaan) · Submissiveness in As-Salat (the prayer)
Narrated Abu Huraira:
حَدَّثَنَا إِسْمَاعِيلُ ، قَالَ حَدَّثَنِي مَالِكٌ ، عَنْ أَبِي الزِّنَادِ ، عَنِ الأَعْرَجِ ، عَنْ أَبِي هُرَيْرَةَ ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " هَلْ تَرَوْنَ قِبْلَتِي هَا هُنَا وَاللَّهِ مَا يَخْفَى عَلَىَّ رُكُوعُكُمْ وَلاَ خُشُوعُكُمْ، وَإِنِّي لأَرَاكُمْ وَرَاءَ ظَهْرِي " .
Allah's Messenger (ﷺ) said, "You see me facing the Qibla; but, by Allah, nothing is hidden from me regarding your bowing and submissiveness and I see you from behind my back."