Sahih Muslim 975
صحيح مسلم#975SahihAnas b. Malik reported:The Messenger of Allah (ﷺ) said: Straighten your rows. for the straightening of a row is a part of the perfection of prayer
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 4:137