Musnad Abu Ya'la al-Mawsili 149:41

Masruq ibn al-Marzuban narrated to us, Ibn al-Mubarak narrated to us, from Yunus ibn Yazid, from al-Zuhri, from Urwah, from Aisha, who said: When the Messenger of Allah (peace and blessings of Allah be upon him) intended to travel, he would cast lots among his wives. Whichever of them her lot came out for, he would take her out with him.