It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that I heard the Messenger of Allah (peace and blessings be upon him) say: The seller and the buyer both have the option to cancel the sale before they separate, or if there is an option in their sale, then if such is the case, the sale becomes final.
Hadith Referenceالسنن المأثورة / باب في البيوع / 233
Hadith Takhrijصحیح بخاری، البيوع، باب اذا كان البائع بالخيار هل يجوز ...... الخ، رقم: 2113، صحیح مسلم، البيوع، باب ثبوت خيار المجلس للمتبايعين، رقم: 1531