أَخْبَرَنَا أَبُو بَكْرِ بْنُ نَافِعٍ، قَالَ حَدَّثَنَا بَهْزُ بْنُ أَسَدٍ، قَالَ حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، عَنْ ثَابِتٍ، عَنْ أَنَسٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ يَقُولُ ‏"‏ اسْتَوُوا اسْتَوُوا اسْتَوُوا فَوَالَّذِي نَفْسِي بِيَدِهِ إِنِّي لأَرَاكُمْ مِنْ خَلْفِي كَمَا أَرَاكُمْ مِنْ بَيْنِ يَدَىَّ ‏"‏ ‏.‏

It was narrated from Anas that the Prophet (PBUH) used to say: "Make your rows straight, make your rows straight, make your rows straight. By the One in Whose Hand is my soul! I can see you behind me as I can see you in front of me." Translation Not Available

Book Ref: Sunan An Nisai Book 10 Hadith 813
Web Ref:  Sunan An Nisai Vol 1 Book 10 Hadith 814