What Can and Cannot Be Used for Prostration
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 41
وَ سَأَلَ اَلْمُعَلَّى بْنُ خُنَيْسٍ أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ: عَنِ اَلصَّلاَةِ عَلَى اَلْقُفْرِ وَ اَلْقِيرِ فَقَالَ «لاَ بَأْسَ بِهِ.
Al-Mu'alla ibn Khunays asked Imam Jafar ibn Muhammad Al-Sadiq عليه السلام about praying on qufr (bare ground or desert soil) and qīr (a type of tar or pitch). Imam عليه السلام said: "There is no issue with it”.
- Ṣaḥīḥ al-Faqīh