The Prophet (ﷺ) said, "Straighten your rows as the straightening of rows is essential for a perfect and correct prayer. "
Sahih al-Bukhari Book 10, Hadith 117
← Previous Hadith The Prophet (ﷺ) said, "The Imam is (appointed) to be followed. So do not differ from him, bow when he bows, and say, "Rabbana-lakal hamd" if he says "Sami`a l-lahu liman hamidah"; and if he prostrates, prostrate (after him), and if he prays sitting, pray sitting all together, and straighten the rows for the prayer, as the straightening of the rows is amongst those things which make your prayer a correct and perfect one. (See Hadith No. 657).

Sahih al-Bukhari Book 10, Hadith 116 Next Hadith → I arrived at Medina and was asked whether I found any change since the days of Allah's Messenger (ﷺ). I said, "I have not found any change except that you do not stand in alignment in your prayers."

Sahih al-Bukhari Book 10, Hadith 118