Although the prohibition of usury is a certainty of Sharia, there is disagreement in two areas regarding the reason for this ruling; some believe that the reason for this ruling, like many rulings, is not stated and cannot be discovered, but on the other hand, some have believed that the reason for this ruling can be discovered. There has also been disagreement in this regard, and some have stated that the reason for the prohibition of usury is the oppression that is achieved through it. This discussion, considering the acceptability of the rule of generalization or allocation of the ruling by reason, has also had jurisprudential fruits; one of these fruits appears in the case of productive usury, with the claim that productive usury is not achieved as oppression, therefore the ruling on the prohibition of usury, the cause of which is the realization of oppression, will not include this case. In the following article, we have examined and criticized the principle of the claim of the causality of oppression for the prohibition of usury using an analytical-descriptive method, and then we have pointed out the impact of the issue on the ruling on productive usury. The result is that it is impossible to prove the causality of oppression for the prohibition of usury, but it is possible to prove its prohibition due to the lack of application of the evidence for the prohibition of usury.