Musannaf Ibn Abi Shayba 3:406

Abu Bakr narrated to us, he said: Isma'il ibn 'Ulayyah narrated to us, from Muhammad ibn Ishaq, from Zur'ah, from Ibrahim, from Khalid ibn al-Lajlaj, who said: Women used to be commanded to sit cross-legged when they sat in prayer, and not to sit as men sit upon their haunches. That is avoided for the woman for fear that something might occur from her.