Sahih Muslim 434
Sahih Muslim · Book 4: The Book of Prayers · Straightening The Rows; The Virtue Of The Front Row And Then The Next; Competing With One Another For The Front Row; The People Of Virtue Should Take Precedence And Be Closest To The Imam
Anas b. Malik reported:
حَدَّثَنَا شَيْبَانُ بْنُ فَرُّوخَ ، حَدَّثَنَا عَبْدُ الْوَارِثِ ، عَنْ عَبْدِ الْعَزِيزِ، - وَهُوَ ابْنُ صُهَيْبٍ - عَنْ أَنَسٍ ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " أَتِمُّوا الصُّفُوفَ فَإِنِّي أَرَاكُمْ خَلْفَ ظَهْرِي " .
The Messenger of Allah (ﷺ) said: Complete the rows, for I can see you behind my back.