Description of the Prayer from Its Beginning to Its End
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 46
وَ سَأَلَ طَلْحَةُ اَلسُّلَمِيُّ أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ: لِأَيِّ عِلَّةٍ تُوضَعُ اَلْيَدَانِ عَلَى اَلْأَرْضِ فِي اَلسُّجُودِ قَبْلَ اَلرُّكْبَتَيْنِ فَقَالَ «لِأَنَّ اَلْيَدَيْنِ بِهِمَا مِفْتَاحُ اَلصَّلاَةِ.
Talha al-Salmi asked Imam Jafar ibn Muhammad Al-Sadiq عليه السلام, "Why do the hands touch the ground before the knees during Sujood (prostration)?" Imam عليه السلام replied: "Because the hands are the key to prayer."
- Ṣaḥīḥ al-Faqīh