The Messenger of Allah ﷺ used to walk through the rows from one side, smoothing our chests and shoulders, saying, "Do not stand unevenly, or your hearts will differ."He would also say, "Indeed, Allah and His angels send blessings upon the front rows."
كان رسول الله ﷺ يتخلل الصف من ناحية يمسح صدورنا ومناكبنا ويقول: لا تختلفوا فتختلف قلوبكم. وكان يقول: إن الله وملائكته يصلون على الصفوف الأول.
Abu Dawud (664) and Nasai (811) both narrated it through Abu Ahwas, from Mansur, from Talha bin Musarrif, from Abdul-Rahman bin Awsaja, from Bara, who mentioned it. Ibn Majah (997) also narrated it through Shuba, who said, "I heard Talha bin Musarrif say, 'I heard Abdul-Rahman bin Awsaja say, I heard Bara bin Azib,'" except that he did not mention the first part of the hadith. For this reason Busiri classified it among the additions and said, "Its isnad is sahih and its narrators are trustworthy." I say, the hadith does not actually meet the criteria for the additions, but it is sahih nonetheless, as Busiri said. Ibn Khuzayma (1551) and Ibn Hibban (2157) also graded it sahih, both from the hadith of Talha bin Musarrif.