If ye do it not...
If ye do it not, take notice of war from God and His Apostle: But if ye turn back, ye shall have your capital sums: Deal not unjustly, and ye shall not be dealt with unjustly.” [The Holy Qur’an, al-Baqarah 2:278-279] Here we note that taking usury is against our beliefs, and is considered to be like staging a war against God and the Prophet . If one repents from doing this heinous act, then he can take back his money without taking any interest.
That is because they say: "Trade is like usury," but God hath permitted trade and forbidden usury. Those who after receiving direction from their Lord, desist, shall be pardoned for the past; their case is for God (to judge); but those who repeat (the offence) are companions of the Fire: they will abide therein (for ever).
God will deprive usury of all blessing, but will give increase for deeds of charity: For He loveth not creatures ungrateful and wicked.” [The Holy Qur’an, al-Baqarah 2:275-276] Here we see usurers depicted like insane men. This may refer to their social behavior since their deeds are similar to mad people. They do not care for sympathy, love, cooperation and the like.
This belief was very popular among the Arabs. As we know, following satanic thoughts will cause one to think differently. Consequently, he will not be able to distinguish right from wrong.