Sahih Muslim 1768
صحيح مسلم#1768SahihJabir reported Allah's Messenger (ﷺ) as saying:The most excellent prayer is that in which the duration of standing is longer
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: 6:197