Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: The Messenger of Allah (peace and blessings be upon him) said: "When fornication and usury (riba) appear openly in a town, they have made lawful for themselves (the punishment mentioned in) the Book of Allah, the Mighty and Majestic."
Hadith Referenceالمعجم الكبير للطبراني / باب الألف / 457