Sahih Muslim 1311
صحيح مسلم#1311SahihAli b. 'Abual-Rahman al-Mu'awi reported:'Abdullah b. Umar saw me playing with pebbles during prayer. After finishing the prayer he forbade me (to do it) and said: Do as the Messenger of Allah (ﷺ) used to do. I said: How did Allah's Messenger (ﷺ) do? He said that he (the Messenger of Allah) sat at tashahhud, placed his right palm on the right thigh and closed all his fingers and pointed with the help of finger next to the thumb, and placed his left palm on his left thigh
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: 5:149