Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates that the Prophet Muhammad (peace and blessings be upon him) said: "The two people involved in a transaction have the right (to cancel the deal) as long as they have not separated from each other." Nafi' reports: It was the practice of Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that when he liked something, he would separate from his companion so that the deal would be finalized in his favor.
Hadith Referenceصحیح ابن حبان / كتاب البيوع / 4912
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «الإرواء» (5/ 153 / 1310)، «أحاديث البيوع»: ق.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط الشيخين