Sahih Muslim 2656
صحيح مسلم#2656SahihIbn Abbas (Allah be pleased with both of them) reported that when Allah's Messenger (ﷺ) came to Medina, he found the Jews observing the fast on the day of Ashura. They (the Jews) were asked about it and they said:It is the day on which Allah granted victory to Moses and (his people) Bani Isra'il over the Pharaoh and we observe fast out of gratitude to Him. Upon this the Messenger of Allah (ﷺ) said: We have a closer connection with Moses than you have, and he commanded to observe fast on this day
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: 13:162