Narrated Ibn 'Umar (RA):

When Allah's Messenger (ﷺ) sat for at-Tashahhud, he placed his left hand on his left knee, and his right hand on his right knee, folded its fingers and pointed with his right index finger. [Reported by Muslim].

وَعَنْ اِبْنِ عُمَرَ ‏-رَضِيَ اَللَّهُ عَنْهُمَا‏- { أَنَّ رَسُولَ اَللَّهِ ‏- صلى الله عليه وسلم ‏-كَانَ إِذَا قَعَدَ لِلتَّشَهُّدِ وَضَعَ يَدَهُ اَلْيُسْرَى عَلَى رُكْبَتِهِ اَلْيُسْرَى , وَالْيُمْنَى عَلَى اَلْيُمْنَى , وَعَقَدَ ثَلَاثَةً وَخَمْسِينَ , وَأَشَارَ بِإِصْبَعِهِ اَلسَّبَّابَةِ } رَوَاهُ مُسْلِمٌ