Sahih al-Bukhari 827
Sahih al-Bukhari · Book 10: Call to Prayers (Adhaan) · The Prophet's Sunna (legal way) for the sitting in the Tashah-hud [in the Salat (prayer)].
Narrated `Abdullah bin `Abdullah:
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ ، عَنْ مَالِكٍ ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ الْقَاسِمِ ، عَنْ عَبْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ ، أَنَّهُ أَخْبَرَهُ أَنَّهُ، كَانَ يَرَى عَبْدَ اللَّهِ بْنَ عُمَرَ ـ رضى الله عنهما ـ يَتَرَبَّعُ فِي الصَّلاَةِ إِذَا جَلَسَ، فَفَعَلْتُهُ وَأَنَا يَوْمَئِذٍ حَدِيثُ السِّنِّ، فَنَهَانِي عَبْدُ اللَّهِ بْنُ عُمَرَ وَقَالَ إِنَّمَا سُنَّةُ الصَّلاَةِ أَنْ تَنْصِبَ رِجْلَكَ الْيُمْنَى وَتَثْنِيَ الْيُسْرَى. فَقُلْتُ إِنَّكَ تَفْعَلُ ذَلِكَ. فَقَالَ إِنَّ رِجْلَىَّ لاَ تَحْمِلاَنِي.
I saw `Abdullah bin `Umar crossing his legs while sitting in the prayer and I, a mere youngster in those days, did the same. Ibn `Umar forbade me to do so, and said, "The proper way is to keep the right foot propped up and bend the left in the prayer." I said questioningly, "But you are doing so (crossing the legs)." He said, "My feet cannot bear my weight."