Sunan Ibn Majah, Volume 2, Book 5, Hadith 976 (DarusSalam) ⓘ

It was narrated that Abu Mas’ud Al-Ansari said: “The Messenger of Allah used to gently pat our shoulders (to make sure the row was straight) at the time of prayer, saying: ‘Keep (the rows) straight, do not differ from one another lest your hearts should suffer from discord. Let those who are forbearing and wise stand closest to me, then those who are next to them, then those who are next to them.’”

حَدَّثَنَا مُحَمَّدُ بْنُ الصَّبَّاحِ، أَنْبَأَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنِ الأَعْمَشِ، عَنْ عُمَارَةَ بْنِ عُمَيْرٍ، عَنْ أَبِي مَعْمَرٍ، عَنْ أَبِي مَسْعُودٍ الأَنْصَارِيِّ، قَالَ كَانَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ يَمْسَحُ مَنَاكِبَنَا فِي الصَّلاَةِ وَيَقُولُ ‏ "‏ لاَ تَخْتَلِفُوا فَتَخْتَلِفَ قُلُوبُكُمْ لِيَلِيَنِي مِنْكُمْ أُولُو الأَحْلاَمِ وَالنُّهَى ثُمَّ الَّذِينَ يَلُونَهُمْ ثُمَّ الَّذِينَ يَلُونَهُمْ ‏" ‏ ‏.‏