The Book of The At-Tatbiq (Clasping One's Hands Together)
12/60. Chapter:
The command to prostrate properly
Sunan an-Nasai
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 (ﷺ) said: "Bow and prostrate properly, for by Allah (SWT) I can see you from behind my back when you bow and prostrate."
Reference : Sunan an-Nasa'i 1117In-book reference : Book 12, Hadith 89English translation : Vol. 2, Book 12, Hadith 1118