Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "When the two parties to a sale disagree, the word of the seller is accepted, and the buyer has the option."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10805
Hadith Gradingمحدثین:حسن لغيره
Hadith Takhrij«حسن لغيره۔ اخرجه احمد 1/ 466۔ الترمذي 1270»