Sayyiduna Samurah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "The buyer and the seller have the option to cancel the deal as long as they have not separated, and whichever of the two is pleased with the sale may take it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10448