Sayyiduna Abdullah bin Umar and Sayyiduna Abdullah bin Abbas (may Allah be pleased with them) both narrate from the Messenger of Allah (peace and blessings be upon him): "Whoever buys goods and the sale becomes due to him has the option as long as his companion has not parted from him; if he wishes he may take it. But if he parts from him, then he has no option."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10440