Sahih Muslim 6766
صحيح مسلم#6766SahihIbn Abbas reported that Allah's Messenger (ﷺ) was asked about the children of the polytheists, whereupon he said:It is Allah alone Who knows what they would be doing according to their creation
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: 46:44