His father told him that he saw the Messenger of Allah ﷺ sitting when praying, putting his right forearm on his right thigh and raising his forefinger, which he had bent slightly, and he was supplicating. (Using translation from Nasāʾī 1274)  

أَنَّهُ رَأَى رَسُولَ اللهِ ﷺ «قَاعِدًا فِي الصَّلَاةِ وَاضِعًا ذِرَاعَهُ الْيُمْنَى عَلَى فَخِذِهِ الْيُمْنَى رَافِعًا إِصْبُعَهُ السَّبَّابَةَ قَدْ أَحْنَاهَا شَيْئًا وَهُوَ يَدْعُو»