كتاب الصلاة
4  
The Book of Prayers
(28)
Chapter: Straightening The Rows; The Virtue Of The Front Row And Then The Next; Competing With One Another For The Front Row; The People Of Virtue Should Take Precedence And Be Closest To The Imam
(28)
باب تَسْوِيَةِ الصُّفُوفِ وَإِقَامَتِهَا وَفَضْلِ الأَوَّلِ فَالأَوَّلِ مِنْهَا وَالاِزْدِحَامِ عَلَى الصَّفِّ الأَوَّلِ وَالْمُسَابَقَةِ إِلَيْهَا وَتَقْدِيمِ أُولِي الْفَضْلِ وَتَقْرِيبِهِمْ مِنَ الإِمَامِ
Sahih Muslim 438 a

Abu Sa'id al-Khudri reported:

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.
حَدَّثَنَا شَيْبَانُ بْنُ فَرُّوخَ، حَدَّثَنَا أَبُو الأَشْهَبِ، عَنْ أَبِي نَضْرَةَ الْعَبْدِيِّ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم رَأَى فِي أَصْحَابِهِ تَأَخُّرًا فَقَالَ لَهُمْ ‏ "‏ تَقَدَّمُوا فَائْتَمُّوا بِي وَلْيَأْتَمَّ بِكُمْ مَنْ بَعْدَكُمْ لاَ يَزَالُ قَوْمٌ يَتَأَخَّرُونَ حَتَّى يُؤَخِّرَهُمُ اللَّهُ ‏"‏ ‏.‏
Reference : Sahih Muslim 438a
In-book reference : Book 4, Hadith 144
USC-MSA web (English) reference : Book 4, Hadith 878
  (deprecated numbering scheme)