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In Islamic Law, the "Kaly - To - Kaly sale" is considered as a null and void contract, but its concept needs to become more clear. AIthoug it is described as a sale under which the both subject matter and price are deferred, but this survey will show that its exact meaning is a sale under which two existing debts are transferred between parties.
Some great Islamic jurists'words protect this view as well, and therefore the subject of consensus will be confined to the case as mentioned abouve. Meanwhile, the consensus could not be taken as a separate reason for the case, because there are quoted words from the Great Prophet here.
On the other hand, it is possible to say that this kind of contract is not a "Sale" but a "contract for sale".
In the begining of the survey, there is a short words on the matter from the point of Civil Code's view.