Musannaf Ibn Abi Shayba 35:113

Affan narrated to us, Hammam narrated to us, from Qatadah, from al-Hasan, from Samurah, from the Prophet (may Allah bless him and grant him peace), who said: "The two parties to a sale have the option [to rescind] as long as they have not separated." And he mentioned that Abu Hanifah said: "The sale is permissible even if they have not separated."