The Etiquette of Women in Prayer
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 55
وَ رَوَى مُحَمَّدُ بْنُ مُسْلِمٍ عَنْ أَبِي جَعْفَرٍ عَلَيْهِ اَلسَّلاَمُ قَالَ: «لَيْسَ عَلَى اَلْأَمَةِ قِنَاعٌ فِي اَلصَّلاَةِ وَ لاَ عَلَى اَلْمُدَبَّرَةِ قِنَاعٌ فِي اَلصَّلاَةِ وَ لاَ عَلَى اَلْمُكَاتَبَةِ إِذَا اِشْتَرَطَ عَلَيْهَا مَوْلاَهَا قِنَاعٌ فِي اَلصَّلاَةِ وَ هِيَ مَمْلُوكَةٌ حَتَّى تُؤَدِّيَ جَمِيعَ مُكَاتَبَتِهَا وَ يَجْرِي عَلَيْهَا مَا يَجْرِي عَلَى اَلْمَمْلُوكِ فِي اَلْحُدُودِ كُلِّهَا.
Muhammad ibn Muslim narrated from Imam Muhammad ibn Ali Al-Baqir عليه السلام who said: "There is no obligation for a slave woman (amā) to wear a headcover (qina'ah) in prayer, nor for a woman who is 'mukātabah' (a slave who has entered into a contract to pay for her freedom) if her master has not required it as part of the terms of her contract, until She has fulfilled all the terms of her contract. The same rules that apply to a slave in all legal matters apply to her as well."
- Ṣaḥīḥ al-Faqīh, p. 51