Abu Dawood: Hadith 988

"Abd Allah b. "Umar saw me playing with pebbles during prayer. When he finished his prayer, he forbade me (to do so) and said: Do as the Apostle (ﷺ) used to do. I asked him: How would the Messenger of Allah (ﷺ) do? He said: When he sat during the prayer (for reciting the tashahhud), he placed his right hand on his right thigh, and clenched all his fingers, and pointed with the finger which is adjacent to the thumb, and he placed his left hand on his left thigh.