Sahih Muslim Book - 5, Hadith - 1311

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ مُسْلِمِ بْنِ أَبِى مَرْيَمَ عَنْ عَلِىِّ بْنِ عَبْدِ الرَّحْمَنِ الْمُعَاوِىِّ أَنَّهُ قَالَ رَآنِى عَبْدُ اللَّهِ بْنُ عُمَرَ وَأَنَا أَعْبَثُ بِالْحَصَى فِى الصَّلاَةِ فَلَمَّا انْصَرَفَ نَهَانِى 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 فِى الصَّلاَةِ وَضَعَ كَفَّهُ الْيُمْنَى عَلَى فَخِذِهِ الْيُمْنَى وَقَبَضَ أَصَابِعَهُ كُلَّهَا وَأَشَارَ بِإِصْبَعِهِ الَّتِى تَلِى الإِبْهَامَ وَوَضَعَ كَفَّهُ الْيُسْرَى عَلَى فَخِذِهِ الْيُسْرَى.

It was narrated from 'Ali bin 'Abdur-Rahman Al-Mu'awi that he said: "'Abdullah bin 'Umar saw me playing with the pebbles while in prayer. When he had finished he told me not to do that. He said: 'Do what the Messenger of Allah (s.a.w) used to do.' I said: 'What did the Messenger of Allah (s.a.w) do?' He said: 'When he sat (in Tashah-hud) during the prayer, he placed his right hand on his right thigh and clenched all his fingers, and pointed with the finger that is next to the thumb, and he put his left hand on his left thigh."'