Musnad Ahmad 1156:67

'Abd al-Rahman ibn Mahdi narrated to us, from Sufyan, from Habib, from Wahb, the freed slave of Abu Ahmad, from Umm Salamah, that the Messenger of Allah (peace and blessings of Allah be upon him) entered upon her while she was covering her head (with a khimar), and he said: "A fold, or two folds."