It was narrated that Umm Salamah said:
“The Messenger of Allah ﷺ was asked about how long a woman’s hem should hang down. He said: ‘A hand span.’ I said: ‘But then (her legs and feet) will be uncovered.’ He said: ‘Then a forearm’s length, but no more than that.’”

حَدَّثَنَا أَبُو بَكْرٍ، حَدَّثَنَا الْمُعْتَمِرُ بْنُ سُلَيْمَانَ، عَنْ عُبَيْدِ اللَّهِ بْنِ عُمَرَ، عَنْ نَافِعٍ، عَنْ سُلَيْمَانَ بْنِ يَسَارٍ، عَنْ أُمِّ سَلَمَةَ، قَالَتْ سُئِلَ رَسُولُ اللَّهِ ـ ﷺ ـ كَمْ تَجُرُّ الْمَرْأَةُ مِنْ ذَيْلِهَا قَالَ " شِبْرًا " . قُلْتُ إِذًا يَنْكَشِفَ عَنْهَا . قَالَ ذِرَاعٌ لاَ تَزِيدُ عَلَيْهِ " .