It is narrated from Hazrat Samurah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: The seller and the buyer have the option to cancel the sale as long as they have not separated from each other.
Hadith Referenceمسند احمد / أول مسند البصريين / 20142
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد ضعيف، الحسن البصري لم يصرح بسماعه