حَدَّثَنَا 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 up for prayer, he took it in his right hand, then turned and said, "Stand straight and straighten your rows." Then he took it in his left hand and said, "Stand straight and straighten your rows."