Sahih al-Bukhari 2109

Abu al-Numan narrated to us: Hammad ibn Zayd narrated to us: Ayyub narrated to us, from Nafi, from Ibn Umar, may Allah be pleased with them both, who said: The Prophet, peace and blessings be upon him, said: “The buyer and seller have the option as long as they have not separated, or until one of them tells the other to choose.” The narrator added: “Or perhaps he said that it is a sale with an option.”