Sayyiduna Nu’man bin Bashir (may Allah be pleased with him) says: The Messenger of Allah (peace and blessings be upon him) used to straighten our rows just as the shafts of arrows are straightened, until when he thought that we had learned this from him and understood this method, one day he turned towards us and saw that a man’s chest was protruding forward. At that time, the Messenger of Allah (peace and blessings be upon him) said: You will certainly straighten your rows, or Allah the Exalted will create discord between your faces.