Musannaf Ibn Abi Shayba 4:678

Abu Bakr ibn Ayyash narrated to us, from Abu Ishaq, from Hubayrah, from Ali, who said: When the last ten [days of Ramadan] would enter, the Prophet (peace be upon him) would wake his family and raise the *mi'zar* (waist-wrapper). It was said to Abu Bakr, "What is raising the *mi'zar*?" He said, "Abstaining from women."