Al-Kāfi - Volume 4 > Kinds of Dresses and Ornaments Permissible or Detestable for a Female Pilgrim in the State of al-’ Ihram
Hadith #11

11ـ حُمَيْدُ بْنُ زِيَادٍ عَنِ ابْنِ سَمَاعَةَ عَنْ غَيْرِ وَاحِدٍ عَنْ أَبَانٍ عَنْ مُحَمَّدٍ الْحَلَبِيِّ قَالَ سَأَلْتُ أَبَا عَبْدِ الله (عَلَيْهِ السَّلاَم) عَنِ الْمَرْأَةِ إِذَا أَحْرَمَتْ أَ تَلْبَسُ السَّرَاوِيلَ قَالَ نَعَمْ إِنَّمَا تُرِيدُ بِذَلِكَ السُّتْرَةَ.

11. Humayd ibn Ziyad has narrated from ibn Sama‘ah from more than one person from Aban ibn ‘Uthman from al-Halabiy who has said the following: “I once asked abu ‘Abd Allah, ‘Alayhi al-Salam, about the case of a woman who is in the state of Ihram: if she can wear trousers. He (the Imam) said, ‘Yes, she can do so because she needs it for covering.’”