Messenger of Allah 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."  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ هَلْ تَرَوْنَ قِبْلَتِي هَا هُنَا وَاللَّهِ مَا يَخْفَى عَلَىَّ رُكُوعُكُمْ وَلاَ خُشُوعُكُمْ وَإِنِّي لأَرَاكُمْ وَرَاءَ ظَهْرِي  

The Prophet ﷺ said, "Perform the bowing and the prostrations properly. By Allah, I see you from behind me (or from behind my back) when you bow or prostrate."  

عَنِ النَّبِيِّ ﷺ قَالَ أَقِيمُوا الرُّكُوعَ وَالسُّجُودَ فَوَاللَّهِ إِنِّي لأَرَاكُمْ مِنْ بَعْدِي وَرُبَّمَا قَالَ مِنْ بَعْدِ ظَهْرِي إِذَا رَكَعْتُمْ وَسَجَدْتُمْ