Sahih Muslim 6681
صحيح مسلم#6681SahihJundub reported that Allah's Messenger (ﷺ) stated that a person said:Allah would not forgive such and such (person). Thereupon Allah the Exalted and Glorious, said: Who is he who adjures about Me that I would not grant pardon to so and so; I have granted pardon to so and so and blotted out his deeds (who took an oath that I would not grant pardon to him)
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: 45:178