عَن النُّعْمَانِ بْنِ بَشِيرٍ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُسَوِّي صُفُوفَنَا حَتَّى كَأَنَّمَا يُسَوِّي بِهَا الْقِدَاحَ حَتَّى رَأَى أَنَّا قَدْ عَقَلْنَا عَنْهُ ثُمَّ خَرَجَ يَوْمًا فَقَامَ حَتَّى كَادَ أَنْ يُكَبِّرَ فَرَأَى رَجُلًا بَادِيًا صَدْرُهُ مِنَ الصَّفِّ فَقَالَ: «عِبَادَ اللَّهِ لَتُسَوُّنَّ صُفُوفَكُمْ أَوْ لَيُخَالِفَنَّ اللَّهُ بَيْنَ وُجُوهِكُمْ» . رَوَاهُ مُسلم

Anas said

The iqama* had been uttered and God’s Messenger faced us and said, “Make your rows straight and stand close together, for l can see you behind my back.” * A repetition of the words of the call to prayer after the worshippers have taken their places with the addition of a statement that the time of prayer has come.Bukhari transmitted it. In the version given by Bukhari and Muslim he said, “Make the rows perfect, for I can see you behind my back."