The Messenger of Allah ﷺ used to straighten our rows. One day he came out and saw a man whose chest was protruding beyond the rest of the people. He said, "Straighten your rows, or Allah will cause your faces to differ."
حدثنا قتيبة حدثنا أبو عوانة عن سماك بن حرب
كان رسول الله ﷺ يسوي صفوفنا فخرج يوما فرأى رجلا خارجا صدره عن القوم فقال لتسون صفوفكم أو ليخالفن الله بين وجوهكم
Agreed upon [by Bukhari and Muslim]. Muslim narrated it in the Book of Prayer, chapter on straightening the rows and establishing them etc., hadith no. 436, from Qutayba, and Bukhari in the Book of Adhan, chapter on straightening the rows at the start of prayer and afterward, hadith no. 717, both from the hadith of Numan bin Bashir.On this topic there are also narrations from Jabir bin Samura [Muslim, hadith no. 430], Bara [Abu Dawud, hadith no. 664], Jabir bin Abdullah [Ahmad, 3/322], Anas [Muslim, hadith nos. 433, 434], Abu Hurairah [Bukhari, hadith no. 615, and Muslim, hadith no. 437], and Ayesha [Ibn Majah, hadith no. 995], "Completing the prayer includes establishing the row properly."The hadith of Umar is found in Muwatta, 1/173, along with the hadith of Ali and Uthman.