كتاب الْمَسَاجِدِ وَمَوَاضِعِ الصَّلاَةِ
5  
The Book of Mosques and Places of Prayer
(21)
Chapter: The description of the sitting during the prayer, and how the hands are to be placed on the thighs
(21)
باب صِفَةِ الْجُلُوسِ فِي الصَّلاَةِ وَكَيْفِيَّةِ وَضْعِ الْيَدَيْنِ عَلَى الْفَخِذَيْنِ ‏
Sahih Muslim 579 a

Abdullah b. Zubair narrated on the authority of his father:

When the Messenger of Allah (ﷺ) sat in prayer. he placed the left foot between his thigh and shank and stretched the right foot and placed his left hand on his left knee and placed his right hand on his right thigh, and raised his finger.
حَدَّثَنَا مُحَمَّدُ بْنُ مَعْمَرِ بْنِ رِبْعِيٍّ الْقَيْسِيُّ، حَدَّثَنَا أَبُو هِشَامٍ الْمَخْزُومِيُّ، عَنْ عَبْدِ الْوَاحِدِ، - وَهُوَ ابْنُ زِيَادٍ - حَدَّثَنَا عُثْمَانُ بْنُ حَكِيمٍ، حَدَّثَنِي عَامِرُ بْنُ عَبْدِ اللَّهِ بْنِ الزُّبَيْرِ، عَنْ أَبِيهِ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا قَعَدَ فِي الصَّلاَةِ جَعَلَ قَدَمَهُ الْيُسْرَى بَيْنَ فَخِذِهِ وَسَاقِهِ وَفَرَشَ قَدَمَهُ الْيُمْنَى وَوَضَعَ يَدَهُ الْيُسْرَى عَلَى رُكْبَتِهِ الْيُسْرَى وَوَضَعَ يَدَهُ الْيُمْنَى عَلَى فَخِذِهِ الْيُمْنَى وَأَشَارَ بِإِصْبَعِهِ ‏.‏
Reference : Sahih Muslim 579a
In-book reference : Book 5, Hadith 145
USC-MSA web (English) reference : Book 4, Hadith 1201
  (deprecated numbering scheme)