حَدَّثَنَا مُسْلِمُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا أَبَانُ، عَنْ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏رُصُّوا صُفُوفَكُمْ وَقَارِبُوا بَيْنَهَا وَحَاذُوا بِالأَعْنَاقِ فَوَالَّذِي نَفْسِي بِيَدِهِ إِنِّي لأَرَى الشَّيْطَانَ يَدْخُلُ مِنْ خَلَلِ الصَّفِّ كَأَنَّهَا الْحَذَفُ ‏"

Narrated Anas ibn Malik

Align your rows, bring them close together, and keep your necks aligned. By Him in Whose hand my soul is, I indeed see the devil entering through the gaps in the row as if he were a small black sheep.