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
← Previous Hadith The Prophet (ﷺ) said, "Martyrs are those who die because of drowning, plague, an Abdominal disease, or of being buried alive by a falling building." And then he added, "If the people knew the Reward for the Zuhr prayer in its early time, they would race for it. If they knew the reward for the `Isha' and the Fajr prayers in congregation, they would join them even if they had to crawl. If they knew the reward for the first row, they would draw lots for it."

Sahih al-Bukhari Book 10, Hadith 115 Next Hadith → 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