According to the universal consensus (ijma) of search-discovered classical Islamic scholarship, Riba (الربا) is the Quranically-prohibited act of receiving an unjust, predetermined increase or excess in a transaction, most commonly defined as interest on a debt. The linguistic root ر-ب-و means 'to increase' or 'grow,' but as Al-Tabari clarifies, its Quranic usage refers specifically to an exploitative growth that lacks any genuine, risk-based economic counterpart. Ibn Kathir's tafsir on the definitive verses (Al-Baqarah 2:275-279) explains that Riba is so severe it constitutes a declaration of 'war from Allah and His Messenger,' a warning unparalleled for other sins. Al-Qurtubi provides the juridical framework, distinguishing it from permissible trade (Bay'), which involves risk and real assets, whereas Riba is a guaranteed, risk-free return on money alone. This synthesis across all Quranic verses and scholarly traditions establishes Riba as an act of economic injustice (zulm) that destroys blessings, concentrates wealth, and undermines social cooperation, contrasting it sharply with charity (Sadaqah), which Allah blesses and causes to grow. Contemporary Islamic finance is entirely built upon creating ethical alternatives to this absolute prohibition.