Sahih Bukhari Volume 3, Book 34, Hadith Number 301.

Narated By ‘Abdullah bin Abu Aufa : A man displayed some goods in the market and swore by Allah that he had been offered so much for that, that which was not offered, and he said so, so as to cheat a Muslim. On that occasion the following Verse was revealed: “Verily! Those who purchase a small gain at the cost of Allah’s covenant and their oaths (They shall have no portion in the Hereafter… etc.)’ (3.77)