Sahih Muslim 256
صحيح مسلم#256SahihIt is reported on the authority of 'Abdullah that the Messenger of Allah observed:The best of' the deeds or deed is the (observance of) prayer at its proper time and kindness to the parents
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: 1:162