Simak binHarb narrated that he heard Nu'man bin Bashir say:
"TheMessengerof Allah (ﷺ) used to straighten the rows until he madethem like aspear or an arrow-shaft. Once he saw a man's chest(sticking out)so the Messenger of Allah (ﷺ) said: 'Make your rowsstraight orAllah will create division among you.'"
English reference: Vol. 1, Book 5, Hadith 994
Arabic reference: Book 5, Hadith 1047