It wasnarrated that Abu Mas'ud Al-Ansari said:
"The Messenger ofAllah(ﷺ) used to gently pat our shoulders (to make sure the row wasstraight) at the time of prayer, saying: 'Keep (the rows) straight,donot differ from one another lest your hearts should suffer fromdiscord. Let those who are forbearing and wise stand closest to me,then those who are next to them, then those who are next to them.'"
English reference: Vol. 1, Book 5, Hadith 976
Arabic reference: Book 5, Hadith 1029