[azth]

There is zero disagreement that interest (and more generally, "riba") is forbidden. Just a couple of references (there are way more):

From the Quran:

* http://quran.com/2/275

* http://quran.com/4/161

From the Hadith:

* The Prophet, Peace be upon him, said: "There will certainly come a time for mankind when everyone will take riba and if he does not do so, its dust will reach him."

* The Prophet, Peace be upon him, cursed the receiver and the payer of interest, the one who records it and the two witnesses to the transaction and said: "They are all alike [in guilt]."