Anas (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) said, "Keep your rows straight (during Salat in congregation), for keeping the rows straight is part of the perfection of Salat."[Al-Bukhari and Muslim]. (ES)
App reference (ES): Book 9, Hadith 97 (ES)
Arabic/English book reference (ES): Book 9, Hadith 1087 (ES)