Sahih Bukhari

Narrated `Abdullah bin Abu `Aufa:A man displayed some goods in the market and took a false oath that he had been offered so much for them though he was not offered that amount Then the following Divine Verse was revealed:-- ""Verily! Those who purchase a little gain at the cost of Allah's covenant and their oaths . . . Will get painful punishment."" (3.77) Ibn Abu `Aufa added, ""Such person as described above is a treacherous Riba eater (i.e. eater of usury)