Sahih al-Bukhari, Volume 1, Book 11, Hadith 690 (USC-MSA) ⓘ
Narrated Anas bin Malik: The Prophet said, "Straighten your rows as the straightening of rows is essential for a perfect and correct prayer. "
حَدَّثَنَا أَبُو الْوَلِيدِ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " سَوُّوا صُفُوفَكُمْ فَإِنَّ تَسْوِيَةَ الصُّفُوفِ مِنْ إِقَامَةِ الصَّلاَةِ " .
also referenced under: Book 10, Hadith 117 (In-Book) & Hadith 723 (DarusSalam)