Sahih Muslim Book 4, Hadith 142
Abu 'Awana reported this hadith with the same chain of transmitters.
The Messenger of Allah (may peace-be upon him) used to straighten our rows as it lie were straightening an arrow with their help until be saw that we had learnt it from him. One day he came out, stood up (for prayer) and was about to say: Allah is the Greatest, when he saw a man, whose chest was bulging out from the row, so he said: Servants of Allah, you hint straighten your rows or Allah would create dissension amongst you.
The Messenger of Allah (ﷺ) said: If the people were to know what excellence is there in the Adhan and in the first row, and they could not (get these opportunities) except by drawing lots, they would have definitely done that. And if they were to know what excellence lies in joining the prayer in the first takbir (prayer), they would have vied with one another. And if they were to know what excellence lies in the night prayer and morning prayer, they would have definitely come even if crawling (on their knees).