Musnad Ahmad 1153:368

Surayj narrated to us, Abu Ma'shar narrated to us, from Hisham ibn 'Urwah, from his father, from 'Aishah, who said: "When ten [days] of Ramadan remained, the Messenger of Allah (may Allah bless him and grant him peace) would tighten his waist-wrapper and withdraw from his wives."