The Messenger of Allah ﷺ used to straighten our rows as carefully as arrows are straightened. Once he noticed a man whose chest was protruding from the line, and I saw the Prophet ﷺ say, "You will straighten your rows, or Allah will set your faces against one another."
أخبرنا قتيبة بن سعيد قال أنبأنا أبو الأحوص عن سماك
كان رسول الله ﷺ يقوم الصفوف كما تقوم القداح فأبصر رجلا خارجا صدره من الصف فلقد رأيت النبي ﷺ يقول لتقيمن صفوفكم أو ليخالفن الله بين وجوهكم
No references are available.
Reported by Muslim, in the Book of Prayer, chapter on straightening the rows and establishing them and the merit of the first row and then the next, and so on, hadith no. 128/436, on the authority of Qutayba, with the same wording. It is also found in Al-Kubra, hadith no. 884.