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 (PBUH)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."' Translation Not Available

Book Ref: Sunan An Nisai Book 10 Hadith 814
Web Ref:  Sunan An Nisai Vol 1 Book 10 Hadith 815