Musannaf Ibn Abi Shayba 13:2614

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from ‘Abdullah ibn Abi al-Safar, from al-Sha’bi, from Shurayh, he said: The two parties to a sale have the option [to rescind or confirm] as long as they have not separated.