All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Getting a rebate on the amount of your debt for hastening the repayment of that loan is known among the scholars as: "Rebate the debt and I pay before deadline."
It is reported in the Maaliki Book: "Al-Fawakih Al-Dawani": 'And it is unlawful to make a discount on the loan against paying it before its deadline.'
So, this way of rebating the debt is not permissible according to the majority of the Muslim scholars. But if there is no binding pre-condition regarding the payment of all payments before the end of the deadline, then there is no objection to such a transaction.
Allaah Knows best.