What Can and Cannot Be Used for Prostration
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 41
وَ سَأَلَ عَلِيُّ بْنُ يَقْطِينٍ أَبَا اَلْحَسَنِ اَلْأَوَّلَ عَلَيْهِ اَلسَّلاَمُ: عَنِ اَلرَّجُلِ يَسْجُدُ عَلَى اَلْمِسْحِ وَ اَلْبِسَاطِ فَقَالَ «لاَ بَأْسَ إِذَا كَانَ فِي حَالِ اَلتَّقِيَّةِ.
Ali ibn Yaqtin asked Imam Abu al-Hasan al-Awwal عليه السلام about a man prostrating on a misḥ (a type of mat or rug) and on a carpet. The Imam said: "There is no issue if it is in a situation of taqiyya (precautionary dissimulation to protect oneself)."
- Ṣaḥīḥ al-Faqīh, p. 41