Abdullah bin Umar reported,

When the Messenger of Allah ﷺ sat for the tashahhud, he would place his left hand on his left knee and his right hand on his right knee, form the number fifty-three with his fingers, and point with his index finger.

Muslim 1310

Sahih

و حدثنا عبد بن حميد حدثنا يونس بن محمد حدثنا حماد بن سلمة عن أيوب عن نافع

عن ابن عمر

أن رسول الله ﷺ كان إذا قعد في التشهد وضع يده اليسرى على ركبته اليسرى ووضع يده اليمنى على ركبته اليمنى وعقد ثلاثة وخمسين وأشار بالسبابة

مسلم 1310صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Muslim
Book
Mosques and places of prayer
Chapter
Description of sitting in prayer and how to place the hands on the thighs
Numbering
Darussalam 1310
Muslim 1310