Sahih Muslim 972
صحيح مسلم#972SahihAbu Mas'ud reported:The Messenger of Allah (may peace he upon him) used to touch our shoulders in prayer and say: Keep straight, don't be irregular, for there would be dissension in your hearts. Let those of you who are sedate and prudent be near me, then those who are next to them, then those who are next to them. Abu Mas'ud said: Now-a-days there is much dissension amongst you
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: 4:134