بُلُوغُ الْمَرَامِ
Bulugh al-Maram 407
The Book of Prayer
وَعَنْ أَبِي سَعِيدٍ اَلْخُدْرِيِّ - رضى الله عنه - { أَنَّ رَسُولَ اَللَّهِ - صلى الله عليه وسلم -رَأَى فِي أَصْحَابِهِ تَأَخُّرًا. فَقَالَ: تَقَدَّمُوا فَائْتَمُّوا بِي, وَلْيَأْتَمَّ بِكُمْ مَنْ بَعْدَكُمْ } رَوَاهُ مُسْلِم ٌ [1] .
Narrated Abu Sa'id al-Khudri (RA): When Allah's Messenger (ﷺ) saw a tendency among his Companions of going to the back he said, "Come forward and follow my lead and let those behind you follow you." [Reported by Muslim].
Sunnah.com reference: Book 2, Hadith 312