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]. (ID)
App reference (ID): Book 9, Hadith 97 (ID)
Arabic/English book reference (ID): Book 9, Hadith 1087 (ID)