The Etiquette of Women in Prayer
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 55
وَ سَأَلَ يُونُسُ بْنُ يَعْقُوبَ أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ: عَنِ اَلرَّجُلِ يُصَلِّي فِي ثَوْبٍ وَاحِدٍ قَالَ «نَعَمْ» قَالَ قُلْتُ فَالْمَرْأَةُ قَالَ «لاَ وَ لاَ يَصْلُحُ لِلْحُرَّةِ إِذَا حَاضَتْ إِلاَّ اَلْخِمَارُ إِلاَّ أَنْ لاَ تَجِدَهُ.
Yunus ibn Ya'qub asked Imam Jafar ibn Muhammad Al-Sadiq عليه السلام about a man who prays in one garment. Imam عليه السلام said: "Yes." He then asked: "What about a woman?" Imam عليه السلام said: "No, and it is not proper for a free woman (Hurr) to pray when she menstruates except with a khimar (headscarf), unless She does not find it."
- Ṣaḥīḥ al-Faqīh, p. 51