The Book of Leading the Prayer (Al-Imamah)
10/27. Chapter:
Hoe many times should he say "Make your rows straight?"
Sunan an-Nasai
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 (ﷺ) 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."
Reference : Sunan an-Nasa'i 813In-book reference : Book 10, Hadith 37English translation : Vol. 1, Book 10, Hadith 814