بُلُوغُ الْمَرَامِ
Bulugh al-Maram 210
The Book of Prayer
وَعَنْ أُمِّ سَلَمَةَ - رَضِيَ اَللَّهُ عَنْهَا- ; أَنَّهَا سَأَلَتْ اَلنَّبِيِّ - صلى الله عليه وسلم -{ أَتُصَلِّي اَلْمَرْأَةُ فِي دِرْعٍ وَخِمَارٍ , بِغَيْرِ إِزَارٍ ? قَالَ : "إِذَا كَانَ اَلدِّرْعُ سَابِغًا يُغَطِّي ظُهُورَ قَدَمَيْهَا } أَخْرَجَهُ أَبُو دَاوُدَ وَصَحَّحَ اَلْأَئِمَّةُ وَقْفَهُ . [1]
Narrated Umm Salamah (RA): She asked the Prophet (ﷺ), "Can a woman pray in a long dress and a veil without wearing a lower garment?" He replied, "If the long dress is ample and covers the surface of her feet." [Reported by Abu Dawud and the Imams graded it Mawquf (a saying of Umm Salamah)].
Sunnah.com reference: Book 2, Hadith 73