ENOfficial
It was narrated from Ibn ‘Umar that the Prophet (ﷺ) used to sit during prayer, putting his hands on his knees and raising his right finger which was next to his thumb, supplicating with it, and with his left hand (spread out) on his knee.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مُحَمَّدُ بْنُ يَحْيَى، وَالْحَسَنُ بْنُ عَلِيٍّ، وَإِسْحَاقُ بْنُ مَنْصُورٍ، قَالُوا حَدَّثَنَا عَبْدُ الرَّزَّاقِ، حَدَّثَنَا مَعْمَرٌ، عَنْ عُبَيْدِ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ النَّبِيَّ ـ صلى الله عليه وسلم ـ كَانَ إِذَا جَلَسَ فِي الصَّلاَةِ وَضَعَ يَدَيْهِ عَلَى رُكْبَتَيْهِ وَرَفَعَ إِصْبَعَهُ الْيُمْنَى الَّتِي تَلِي الإِبْهَامَ فَيَدْعُو بِهَا وَالْيُسْرَى عَلَى رُكْبَتِهِ بَاسِطَهَا عَلَيْهَا .
sunnah.com