Can I drive my friend's car or let him pick me up, if I knew that he bought his car with interest (Riba)?
Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
It is your duty to advise your friend and urge him to repent from dealing with Riba (usury and interest). So, if he accepts your advice, there is no harm to drive his car or to benefit from it.
But, if he refuses, then there will be no good for you to befriend him.
Anyway, there is no objection to use his car, although it is detested to benefit from property of usurers.
Allah knows best.
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