Sahih Muslim Book 4, Hadith 145
The Messenger of Allah (ﷺ) saw people at the end of the mosque, and then the (above-mentioned hadith) was narrated.
The Messenger of Allah (ﷺ) saw (a tendency ) among his Companions to go to the back, so he said to them: Come forward and follow my lead, and let those who come after you follow your lead. People will continue to keep back till Allah will put them at the back.
The Messenger of Allah (ﷺ) said: If you were to know, or if they were to know, what (excellence) lies in the first rows, there would have been drawing of lots (for filling them) ; and Ibn Harb said: For (occupying) the first row there would have been drawing of lots.