Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates that the Prophet (peace and blessings be upon him) said: "The buyer and the seller have the option to cancel the deal before they separate, or (until) one of them says to the other: 'Choose.'" And sometimes he said: "or there is an option."
(b) In the narration of al-Adib, the Messenger of Allah (peace and blessings be upon him) said: "The buyer and the seller have the option to cancel the deal before they separate, except when the sale between them is one with an option, or he says to his companion: 'Choose.'"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10434