Musannaf Ibn Abi Shayba 35:111

Hashim ibn al-Qasim narrated to us, Ayyub ibn Utbah narrated to us, Abu Kathir al-Suhaymi narrated to us, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The two parties to a sale have the option (to rescind) their sale as long as they have not separated, or unless their sale was by mutual choice."