one day I prayed by the side of Anas b. Malik. He said ; Do you know why this stick is placed here ? I said : No, by Allah. He said; The Messenger of Allah ﷺ used to put his hand upon it and say: Keep straight and straighten your rows. (Using translation from Abū Dāʾūd 669)   

هَلْ تَدْرِي لِمَ صُنِعَ هَذَا الْعُودُ؟ قُلْتُ لَا وَاللهِ قَالَ كَانَ رَسُولُ اللهِ ﷺ يَضَعُ عَلَيْهِ يَدَهُ فَيَقُولُ اسْتَوُوا اعْدِلُوا صُفُوفَكُمْ  

[Machine] Indeed, the Messenger of Allah ﷺ, when he stood for prayer, he would take hold of his right hand, then turn around and say, "Straighten your rows, align your rows." Then he would take hold of his left hand and say, "Straighten your rows, align your rows." The sheikh, may Allah the Most High have mercy on him, said, "And all other Sunnahs regarding the straightening of the rows and its manner are mentioned in the chapters of leadership, by the will of Allah."  

إِنَّ رَسُولَ اللهِ ﷺ كَانَ إِذَا قَامَ إِلَى الصَّلَاةِ أَخَذَهُ بِيَمِينِهِ ثُمَّ الْتَفَتَ فَقَالَ اعْدِلُوا سَوُّوا صُفُوفَكُمْ ثُمَّ أَخَذَهُ بِيَسَارِهِ فَقَالَ اعْدِلُوا سَوُّوا صُفُوفَكُمْ قَالَ الشَّيْخُ رَحِمَهُ اللهِ تَعَالَى وَسَائِرُ السُّنَنِ فِي تَسْوِيَةِ الصُّفُوفِ وَكَيْفِيَّتِهَا مُخَرَّجَةٌ فِي أَبْوَابِ الْإِمَامَةِ بِمَشِيئَةِ اللهِ