Sahih Muslim 3323
صحيح مسلم#3323SahihAsim reported:I asked Anas b. Malik whether Allah's Messenger (ﷺ) had declared Medina as sacred. He said: Yes. (the area) between so and so. He who made any innovation in it, and further said to me: It is something serious to make any innovation in it (and he who does it) there is upon him the curse of Allah, and that of the angels and of all the people, Allah will not accept from him on the Day of Resurrection either obligatory acts or the surpererogatory acts. Ibn Anas said: Or he accommodates an innovator
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: 15:527