Sahih Muslim 5298
صحيح مسلم#5298SahihAbdullah b. Ka'b reported that his father Ka'b narrated to him that Allah's Messenger (ﷺ) used to eat with three fingers and when he had finished (eating), he licked them
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: 36:172