Praise be to Allah.
We put this question to Shaykh Muhammad ibn Saalih al-Uthaymeen: one of our brothers in Canada is working as a taxi driver, and says that often, after taking on a passenger and commencing the journey, the passenger asks him to stop near a liquor store so that he can buy something from there. Some passengers also ask him to take them to places such as nightclubs. Is it permissible for him to work in this occupation or to accept these fares?
The shaykh, may Allaah preserve him, replied as follows:
No, it is not permissible for him to stop at the liquor store for his passenger to buy some, and it is not permissible for him to take anyone to forbidden clubs, because Allaah says (interpretation of the meaning): Help you one another in al-birr and al-taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression [al-Maaidah 5:2].
And Allaah knows best.