Ibn Abi al-Shuwarab محمد بن عبد الملك بن أبي الشوارب · The Book of Adornment

"The Messenger of Allah was asked how much a woman should let her hem drag. He said: 'A hand span.' She said: 'But then it will uncover her (feet).' He said: 'A forearm's length, and no more than that.'"