أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ أَنْبَأَنَا عَبْدَةُ، عَنْ سَعِيدٍ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ أَتِمُّوا الرُّكُوعَ وَالسُّجُودَ فَوَاللَّهِ إِنِّي لأَرَاكُمْ مِنْ خَلْفِ ظَهْرِي فِي رُكُوعِكُمْ وَسُجُودِكُمْ ‏"‏ ‏.‏

It was narrated from Anas that: The Messenger of Allah (PBUH) said: "Bow and prostrate properly, for by Allah (SWT) I can see you from behind my back when you bow and prostrate." Translation Not Available

Book Ref: Sunan An Nisai Book 12 Hadith 1117
Web Ref:  Sunan An Nisai Vol 2 Book 12 Hadith 1118