Hadith 907
وَفِي رِوَايَةٍ: كَانَ إِذَا جَلَسَ فِي الصَّلَاةِ وَضَعَ يَدَيْهِ عَلَى رُكْبَتَيْهِ وَرَفَعَ أُصْبُعَهُ الْيُمْنَى الَّتِي تلِي الْإِبْهَام يَدْعُو بِهَا وَيَدَهُ الْيُسْرَى عَلَى رُكْبَتِهِ بَاسِطَهَا عَلَيْهَا. رَوَاهُ مُسلم
A version says that when he sat during the prayer he placed his hands on his knees and raised his right finger which is next to the thumb making supplication in this way, while keeping his left hand spread out on his left knee. Muslim transmitted it.