'Ali 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.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ مُسْلِمِ بْنِ أَبِي مَرْيَمَ، عَنْ عَلِيِّ بْنِ عَبْدِ الرَّحْمَنِ الْمُعَاوِيِّ، أَنَّهُ قَالَ رَآنِي عَبْدُ اللَّهِ بْنُ عُمَرَ وَأَنَا أَعْبَثُ بِالْحَصَى فِي الصَّلاَةِ فَلَمَّا انْصَرَفَ نَهَانِي فَقَالَ اصْنَعْ كَمَا كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَصْنَعُ . فَقُلْتُ وَكَيْفَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَصْنَعُ قَالَ كَانَ إِذَا جَلَسَ فِي الصَّلاَةِ وَضَعَ كَفَّهُ الْيُمْنَى عَلَى فَخِذِهِ الْيُمْنَى وَقَبَضَ أَصَابِعَهُ كُلَّهَا وَأَشَارَ بِإِصْبَعِهِ الَّتِي تَلِي الإِبْهَامَ وَوَضَعَ كَفَّهُ الْيُسْرَى عَلَى فَخِذِهِ الْيُسْرَى .
sunnah.com