Musnad Ahmad 1153:901

Affan narrated to us, he said: Abd al-Warith narrated to us, he said: Habib al-Mu'allim narrated to us, from Abu al-Muhazzam, from Abu Hurayrah, from Aisha, that the Prophet, peace and blessings of Allah be upon him, said: "In the hems of women [there is] a span." He said: So Aisha said: "Then their shins will be exposed." And Affan said once: "Their shins." He said: "[Then] a forearm."