Musnad Abu Ya'la al-Mawsili 209:12

Ibn Numayr narrated to us, my father narrated to us, Ubaydullah narrated to us, he said: Nafi’ narrated to me, from Sulayman ibn Yasar, from Umm Salamah, she said: I said, "O Messenger of Allah, what about the women?" He said, "They should let [their garments] down by a span." I said, "O Messenger of Allah, then their [feet] will be uncovered." He said, "Then by a forearm's length, and they should not exceed that."