What is the ruling of Sharia on using inherited money (8,000 Euros) from a non-Muslim father to pay off part of an interest-based student loan (15,000 Euros) that was taken before converting to Islam, knowing that repayment of the loan is obligatory if studies are not completed?

The determining factor is the condition of the heir at the time of the legator's death. If you were a Muslim at the time of your disbelieving father's death, you are not entitled to inherit from him. The money must be returned to the estate to be distributed among his heirs who share his religion. You are not permitted to withhold it or distribute it piecemeal. However, if you were not a Muslim at the time of your father's death, then you inherit from him, and the money becomes rightfully yours. It remains yours even if you convert to Islam later.

If you are unable to dispose of the money, you are not obliged to hand it over to anyone until you receive it. It is not permissible to use it to pay off your loan because it is the property of others. However, you may take your mother's share from it as a benevolent loan if she agrees. If one of the heirs grants you their share, there is no harm in accepting it. A Muslim is rewarded by Allah if they miss out on inheritance due to a difference in religion.