The wives of the Prophet ﷺ asked him about the hem of their garments.He said, "Let it extend a handspan."They replied, "A handspan is not enough to cover what must be concealed."He said, "Then let it extend a forearm's length."So whenever one of them wished to make a dress, she would let it down by a forearm's length and use that as the hem.
حدثنا حجاج أخبرنا شريك عن مطرف عن زيد العمي عن أبي الصديق الناجي
أن نساء النبي ﷺ سألنه عن الذيل فقال اجعلنه شبرا فقلن إن شبرا لا يستر من عورة فقال اجعلنه ذراعا فكانت إحداهن إذا أرادت أن تتخذ درعا أرخت ذراعا فجعلته ذيلا
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Its isnad is sahih. Mutarrif is Ibn Tarif Harithi, whose reliability was already established at 580, and we add here that Ahmad and Abu Hatim confirmed his reliability, and Shafii said, "Ibn Uyayna was not more impressed by anyone than he was by Mutarrif." Bukhari gave his biography in Al-Kabir 4/1/397. The hadith is a repetition of 4683, see also 5173, 5535, and see what follows in the Musnad of Abu Hurairah, 7563.