He -asws said: ‘And when you sit during your performing of the Tashahhud (three or more testimonies), so paste the two knees with the ground and separate between the two a bit, and let the back of your left foot be upon the ground and the back of your right foot be upon the inside of your left foot and your backside to be upon the ground, and the side of your right big toe to be upon the ground. And beware of the sitting upon your two feet, for you would be hurt by that.
And do not sit with part of you upon the (other) part but let yourself be sitting upon the ground, so you should rather happen to be sitting (comfortably), otherwise you would not be patient for the Tashahhud and the supplication’.
[57] عَنْهُ عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ حَمَّادٍ عَنْ حَرِيزٍ عَنْ رَجُلٍ عَنْ أَبِي جَعْفَرٍ ( عليه السلام ) قَالَ قُلْتُ لَهُ فَصَلِّ لِرَبِّكَ وَ انْحَرْ قَالَ النَّحْرُ الِاعْتِدَالُ فِي الْقِيَامِ أَنْ يُقِيمَ صُلْبَهُ وَ نَحْرَهُ From him, from Ahmad Bin Muhammad, from Hammad, from Hareyz, from a man, (It has been narrated) from Abu Ja’far -asws , said, ‘I said to him -asws , ‘(What about) [108:2] Therefore pray Salāt to your Lord and make a sacrifice ?’ He -asws said: ‘The moderation during the standing, that he should straighten his back and his face’.
وَ قَالَ لَا تُكَفِّرْ فَإِنَّمَا يَصْنَعُ ذَلِكَ الْمَجُوسُ وَ لَا تَلَثَّمْ وَ لَا تَحْتَفِزْ وَ لَا تُقْعِ عَلَى قَدَمَيْكَ وَ لَا تَفْتَرِشْ ذِرَاعَيْكَ . And he -asws said: ‘Do not place one hand upon the other, that is what the Magians do, and neither veil your face, nor hold limbs tightly, nor fall upon your feet, nor spread out your arms’.
[58] Amir-ul-Momineen -asws Says: لا يجمع المؤمن يديه في الصلاة و هو قائم يتشبه بأهل الكفر The believers should not put one hand on the other while standing straight in prayers like the disbelievers (do).