This concerns a man who displayed goods for sale in the market and swore by Allah that he had been offered a price for them which he had not in fact been offered, in order to trap one of the Muslims into buying them. So there was revealed, "Indeed, those who purchase a small gain at the cost of the covenant of Allah and their oaths" [Al Imran 3:77].
في أن رجلا أقام سلعة وهو في السوق، فحلف بالله لقد أعطى بها ما لم يعط؛ ليوقع فيها رجلا من المسلمين فنزلت: {إن الذين يشترون بعهد الله وأيمنهم ثمنا قليلا} [سورة آل عمران: ٧٧].