Sahih Muslim 5503
صحيح مسلم#5503SahihJalbir b. Abdullah reported Allah's Messenger (ﷺ) as saying:None of you should lie on his back and place one of his feet upon the other
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: 37:118