سُنَنُ النَّسَائِيِّ
Sunan an-Nasa’i 814
The Book of Leading the Prayer (Al-Imamah)
The Imam encouraging (worshippers) to make the rows solid and stand close to one another
أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، أَنْبَأَنَا إِسْمَاعِيلُ، عَنْ حُمَيْدٍ، عَنْ أَنَسٍ، - رضى الله عنه - قَالَ أَقْبَلَ عَلَيْنَا رَسُولُ اللَّهِ صلى الله عليه وسلم بِوَجْهِهِ حِينَ قَامَ إِلَى الصَّلاَةِ قَبْلَ أَنْ يُكَبِّرَ فَقَالَ أَقِيمُوا صُفُوفَكُمْ وَتَرَاصُّوا فَإِنِّي أَرَاكُمْ مِنْ وَرَاءِ ظَهْرِي .
It was narrated that Anas said: "The Messenger of Allah (ﷺ)turned to face us when he stood up to pray, before he said the Takbir and said: 'Make your rows straight and come close to one another, for I can see you behind my back."'
Sunan an-Nasa'i, 814Sahih (Darussalam)