Is it permissible to benefit from the fare for transporting passengers to the Cave of Thawr instead of the Cave of Hira by mistake, and is the driver sinful?

You do not deserve the fare you received because you did not perform the agreed-upon work. You must bear the responsibility for the mistake in the location. If you are unable to return the fare to the passengers, then donate it on their behalf, as Ibn Taymiyyah and others held that it is permissible to spend money whose owner cannot be identified on matters benefiting the Muslims. As for sin, it does not befall you for a mistake, due to the Prophet's (peace be upon him) saying: "Indeed, Allah has forgiven for my Ummah mistakes and forgetfulness."