Am I sinful for helping my brother pay off a usurious loan for a car he bought and left with me until his return from travel?

Paying back an usurious loan and its interest is considered aiding in the consumption of usury, which is forbidden, based on the Prophet's (peace be upon him) saying: "Allah's Messenger (peace be upon him) cursed the one who consumes Riba (usury), the one who pays it, the one who writes it down, and the two who witness it." And he said: "They are all equal (in sin)." The borrower must repent and return the borrowed money. If it is possible for him not to return the interest, then he should not return it. He should also hasten to accelerate repayment if that eliminates the interest.