Musannaf Ibn Abi Shayba 9:1692

Abu al-Ahwas narrated to us, from Mansur, from Abu Wa'il, from 'Ubayd Allah, who said: The Messenger of Allah (may Allah bless him and grant him peace) forbade that a woman should have physical contact [with another woman] while in a single garment, lest she describe her to her husband.