In earning his living, the Muslim should stick to rules of Shari`ah and he should exert efforts in searching for the halal and steer clear of all what is haram. Muslims have to cooperate in righteousness and morality. In this context, Allah, Most High, says, “… help ye one another unto righteousness and pious duty. Help not one another unto sin and transgression, but keep your duty to Allah. Lo! Allah is severe in punishment.” (Al-Ma’idah: 2)
Focusing more on the question in point, the following is the fatwa issued by the well-known Saudi scholar, Sheikh `Abdullah ibn Jibreen:
“Undoubtedly, taking people to haram (unlawful) places is considered to be a form of rendering assistance in sin and transgression. We advise you not to take these people to places of corruption and bars. You will find other people. This applies whether you take them from these places or to them. Whoever fears Allah and keeps his duty towards Him (Taqwa), Allah will grant him a way-out, so look for other passengers from other places. If it so happens that you are taken unaware, and thereby, take passengers to such places then we do not say that the fare is haram, because it is compensation for your efforts, or for the use of your car.
If you think that you are obliged to do something haram in your work, then look for other work. We ask Allah to make your provision halal.”