Sahih Muslim 7086
صحيح مسلم#7086SahihAnas reported this hadlth through another chain of transmitters and the words are:" It would be said to him: You have told a lie; what had been demanded from you was quite easier than this (the belief in the Oneness of Allah)
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: 52:40