Tafsir Ibn Kathir -> Surah Al-'Imran -> Interest (Riba) is Prohibited

Allah prohibits His believing servants from dealing in Riba and from requiring interest on their capital, just as they used to do during the time of Jahiliyyah. For instance, when the time to pay a loan comes, the creditor would say to the debtor, "Either pay now, or the loan will incur interest.'' If the debtor asks for deferment of the loan, the creditor would require interest and this would occur year after year until the little capital becomes multiplied many times. Allah also commands His servants to have Taqwa of Him so that they may achieve success in this life and the Hereafter. Allah also threatens them with the Fire and warns them against it, saying,

﴿وَاتَّقُواْ النَّارَ الَّتِى أُعِدَّتْ لِلْكَـفِرِينَ - وَأَطِيعُواْ اللَّهَ وَالرَّسُولَ لَعَلَّكُمْ تُرْحَمُونَ ﴾

(And fear the Fire, which is prepared for the disbelievers. And obey Allah and the Messenger that you may obtain mercy.) ﴿3:131,132﴾.