Sunan Abi Dawud 21174
In-book no 670حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا حُمَيْدُ بْنُ الأَسْوَدِ، حَدَّثَنَا مُصْعَبُ بْنُ ثَابِتٍ، عَنْ مُحَمَّدِ بْنِ مُسْلِمٍ، عَنْ أَنَسٍ، بِهَذَا الْحَدِيثِ قَالَ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا قَامَ إِلَى الصَّلاَةِ أَخَذَهُ بِيَمِينِهِ ثُمَّ الْتَفَتَ فَقَالَ " اعْتَدِلُوا سَوُّوا صُفُوفَكُمْ " . ثُمَّ أَخَذَهُ بِيَسَارِهِ فَقَالَ " اعْتَدِلُوا سَوُّوا صُفُوفَكُمْ " .
This tradition has also ben transmitted by Anas through a different chain of transmitters. This version goes: when the Messenger of Allah (ﷺ) stood for prayer, he took it (the stick) in his right hand and turning (to the right side) said; keep straight and straighten your rows. He then took it in his left hand and said; keep straight and straighten your rows.