Riyad as-Salihin #410

An-Nu'man bin Bashir (May Allah be pleased with them) reported: I heard the Messenger of Allah (ﷺ) saying, "Straighten your rows; otherwise, Allah will create dissension among you.".The narration in Muslim is: An-Nu'man bin Bashir (May Allah be pleased with them) said: The Messenger of Allah (ﷺ) directed us to keep our rows as straight as arrows. He continued stressing this until he realized that we had learnt it from him (recognized its significance). One day he came into the mosque and stood up. He was just about to say Takbir (Allah is Greater) when he noticed a man whose chest was projected from the row, so he said, "O slaves of Allah, you must straighten your rows or Allah will certainly put your faces in opposite directions."