Sahih Muslim Book - 4, Hadith - 958

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ عَنْ مَالِكِ بْنِ أَنَسٍ عَنْ أَبِي الزِّنَادِ عَنْ الْأَعْرَجِ عَنْ أَبِي هُرَيْرَةَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ هَلْ تَرَوْنَ قِبْلَتِي هَا هُنَا فَوَاللَّهِ مَا يَخْفَى عَلَيَّ رُكُوعُكُمْ وَلَا سُجُودُكُمْ إِنِّي لَأَرَاكُمْ وَرَاءَ ظَهْرِي.

It was narrated from Abu Hurairah that the Messenger of Allah (s.a.w) said: "Do you think that I face the Qiblah? By Allah, your bowing and prostrating are not hidden from me; I can see you behind my back."