سنن ابن ماجه

Simak bin Harb narrated that he heard Nu’man bin Bashir say: “The Messenger of Allah (ﷺ) used to straighten the rows until he made them like a spear or an arrow-shaft. Once he saw a man’s chest (sticking out) so the Messenger of Allah (ﷺ) said: ‘Make your rows straight or Allah will create division among you.’”