Sunan an-Nasa'i, Volume 2, Book 13, Hadith 1276 (DarusSalam) ⓘ

It was narrated from 'Amir bin Abdullah bin Az-Zubair, from his father, that: When the Messenger of Allah sat to say the tashahhud, he placed his left hand on his left thigh and pointed with his forefinger, and his gaze did not go beyond he finger with which he was pointing.

أَخْبَرَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا يَحْيَى، عَنِ ابْنِ عَجْلاَنَ، عَنْ عَامِرِ بْنِ عَبْدِ اللَّهِ بْنِ الزُّبَيْرِ، عَنْ أَبِيهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا قَعَدَ فِي التَّشَهُّدِ وَضَعَ كَفَّهُ الْيُسْرَى عَلَى فَخِذِهِ الْيُسْرَى وَأَشَارَ بِالسَّبَّابَةِ لاَ يُجَاوِزُ بَصَرُهُ إِشَارَتَهُ ‏.‏