Sahih Muslim 435
Sahih Muslim · Book 4: The Book of Prayers · Straightening The Rows; The Virtue Of The Front Row And Then The Next; Competing With One Another For The Front Row; The People Of Virtue Should Take Precedence And Be Closest To The Imam
Hammam b. Munabbih reported:
حَدَّثَنَا مُحَمَّدُ بْنُ رَافِعٍ ، حَدَّثَنَا عَبْدُ الرَّزَّاقِ ، حَدَّثَنَا مَعْمَرٌ ، عَنْ هَمَّامِ بْنِ مُنَبِّهٍ ، قَالَ هَذَا مَا حَدَّثَنَا أَبُو هُرَيْرَةَ ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم فَذَكَرَ أَحَادِيثَ مِنْهَا وَقَالَ " أَقِيمُوا الصَّفَّ فِي الصَّلاَةِ فَإِنَّ إِقَامَةَ الصَّفِّ مِنْ حُسْنِ الصَّلاَةِ " .
This is what was transmitted to us by Abu Huraira from the Messenger of Allah (ﷺ) and, while making a mention of a few ahadith, said: (The Messengerof Allah directed us thus): Establish rows in prayer, for the making of a row (straight) is one of the merits of prayer.