Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1202
'Abdullah b. Zubair narrated on the authority of his father that when the Messenger of Allah (may peace be upon him) sat for supplication, i. e. tashahhud (blessing and supplication), he placed his right hand on his right thigh and his left hand on his left thigh, and pointed with his forefinger, and placed his thumb on his (milddle) finger, and covered his knee with the palm of his left hand..