Sahih Muslim 1786
صحيح مسلم#1786SahihUbayy b Ka'b reported:By Allah, I know about Lailat-ul Qadr and I know it fully well that it is the twenty-seventh night (during Ramadan) on which the Messenger of Allah (ﷺ) commanded us to observe prayer. (Shu'ba was in doubt about these words:" the night on which the Messenger of Allah [may peace be upon him] commanded us to observe the prayer." This has been transmitted to me by a friend of mine
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: 6:214