Sunnah.com reference : Book 2, Hadith 201English translation : Book 2, Hadith 311Arabic reference : Book 2, Hadith 313
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