He arrived in Madinah and was asked, "What do you find changed among us since the days when you knew the Messenger of Allah ﷺ?"He replied, "I find nothing changed except that you do not straighten your rows."
أنه قدم المدينة، فقيل له: ما أنكرت منا منذ يوم عهدت رسول الله ﷺ؟ قال: ما أنكرت شيئا إلا أنكم لا تقيمون الصفوف.
Bukhari related it in the Book of Adhan (724), through the route of Bashir bin Yasar Ansari, from Anas bin Malik, who mentioned something similar. Bukhari titled this chapter, "The Sin of One Who Does Not Complete the Rows," from which it is understood that he held the obligation of straightening the rows, like the Zahiris. However, it has not been reported from anyone that the prayer of one who differs and does not straighten the rows is invalid. This is supported by the fact that Anas, despite rebuking them, did not command them to repeat the prayer, except for Ibn Hazm, who held the view that the prayer is invalid.