It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "The seller and the buyer have the option (to cancel the transaction) as long as they do not separate, or until one of them says to the other, 'Make your choice.'"
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 5418
Hadith Gradingحکم دارالسلام:إسناده صحيح ، خ : 2107، م :1531.