Bulugh al-Maram 2 The Book of Prayer كتاب الصلاة 197

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

Narrated Ibn ‘Umar (RA): When Allah’s Messenger (صلى الله عليه وسلم) 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].