Riba — commonly translated as interest or usury, broadly any predetermined, guaranteed increase charged on a loan — is prohibited in unusually strong language across five consecutive verses of Surah al-Baqarah (2:275–279), among the most severe warnings on any single topic in the Qur'an.

The passage draws a deliberate contrast: 'Allah has permitted trade and forbidden riba' (2:275). Trade — buying, selling, and investing where both parties share genuine risk and effort — is praised; riba, a fixed charge owed regardless of outcome, is condemned. The chapter goes on to command believers to give up any outstanding riba entirely, warning of serious consequences for those who persist, while promising that whoever repents may keep only their original principal — no more, no less.

This is a foundational teaching to be aware of, not a checklist for auditing every modern financial product yourself. Working out whether a specific contract (a mortgage, a loan, a savings account) involves riba in practice requires reviewing its actual terms with someone qualified in Islamic finance.