Riyad as-Salihin (The Meadows of the Righteous)
by Imam Nawawi
Allah Almighty says, "Those who practise usury will not rise from the grave except as someone driven mad by Shaytan's touch. That is because they say, 'Trade is the same as usury.' But Allah has permitted trade and He has forbidden usury. Whoever is given a warning by his Lord and then desists, can keep what he received in the past and his affair is up to Allah. But all who return to it will be the Companions of the Fire, remaining in it timelessly, forever. Allah obliterates usury but makes sadaqa grow in value!" to His words "O you who believe! Show fear of Allah and forgo any remaining usury." (W2:274-277; H2:275-278)
At-Tirmidhi added, "And the witnesses to it and those who write it down."