First, the usury was prohibited with the following verse:
“O believers! Do not devour usury that doubles and redoubles. Be careful of (your duty to) Allah, that you may be successful in achieving what you want.”(Al-i Imran/ the House of Imran, 3/130)
Redoubling is one of usury’s characteristics. The interest of a loan that starts with 10%, the second year is increased to 21%, the following year to 33% and with time passes the value of the loan itself. The second prohibition of usury was done with the following verses.
O believers! Fear Allah! If you are of the believers relinquish what remains (due) from usury. If you do not do it, then you are in war with Allah and His Messenger. If you repent, then you keep your capital. Neither will you suffer injustice, nor will you be made to suffer injustice. If the debtor is difficulty, then let there be postponement until he is in ease. And it is better for you to that you remit (it) as gifts. Only if you knew!…” (Al-Baqara/The Cow 2/278-280)
In the Ignorance Period the loan taker who was not able to pay back his loan was sold as slave. The last mentioned verse not only prohibited the selling of indebted people as slaves, bur foresaw the prolongation of the predicted period.
 Kurtubi Abu Abdillah Mohammed b. Ahmed el-Ensari, (671/1272), el-Cami li-Ahkami’l-Kur’an, Daru’l-kutubi’l-ilmiyyeh, 1409/1988, b III, p 240. The explanation of the al-Bakara.