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. (Using translation from Ibn Mājah 913)
أَنَّ رَسُولَ اللهِ ﷺ كَانَ «إِذَا جَلَسَ فِي الصَّلَاةِ وَضْعَ يَدَيْهِ عَلَى رُكْبَتَيْهِ وَرَفَعَ إِصْبُعَهُ الَّتِي تَلِي الْإِبْهَامَ يَدْعُو بِهَا وَيَدُهُ الْيُسْرَى عَلَى رُكْبَتَهُ بَاسِطُهَا عَلَيْهَا»