Hadith 201
وَحَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّ الْقَاسِمَ بْنَ مُحَمَّدٍ، أَرَاهُمُ الْجُلُوسَ فِي التَّشَهُّدِ فَنَصَبَ رِجْلَهُ الْيُمْنَى وَثَنَى رِجْلَهُ الْيُسْرَى وَجَلَسَ عَلَى وَرِكِهِ الأَيْسَرِ وَلَمْ يَجْلِسْ عَلَى قَدَمِهِ ثُمَّ قَالَ أَرَانِي هَذَا عَبْدُ اللَّهِ بْنُ عَبْدِ اللَّهِ بْنِ عُمَرَ وَحَدَّثَنِي أَنَّ أَبَاهُ كَانَ يَفْعَلُ ذَلِكَ .
Yahya related to me from Malik from Yahya ibn Said that al-Qasim ibn Muhammad showed them how to sit in the tashahhud, and he kept his right foot vertical and laid his left foot down, and sat on his left haunch not on his foot. Then he said, "Abdullah ibn Abdullah ibn Umar saw me doing this and related to me that his father used to do the same thing
Mauquf Sahih (Salim al-Hilali)
Muwatta Malik 201 · Book 3, Hadith 34