مُوَطَّأُ مَالِكٍ
Muwatta Malik 404
Shortening the Prayer
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ أَتَرَوْنَ قِبْلَتِي هَاهُنَا فَوَاللَّهِ مَا يَخْفَى عَلَىَّ خُشُوعُكُمْ وَلاَ رُكُوعُكُمْ إِنِّي لأَرَاكُمْ مِنْ وَرَاءِ ظَهْرِي .
Yahya related to me from Malik from Abu'z Zinad from al-Araj from Abu Hurayra that the Messenger of Allah, (ﷺ), said, "Do you see the direction I am facing here? By Allah, neither your concentration nor your ruku is hidden from me. I can see you behind my back."
Arabic/English book reference: Book 9, Hadith 73