Does riding with a bus driver who backbites others necessitate participation in sin, despite seeking forgiveness?

Denouncing evil is obligatory according to one's capacity. If you are able to denounce backbiting, then do so. But if you fear harm or are unable to leave the gathering, then busy yourself with dhikr (remembrance of Allah) and istighfar (seeking forgiveness). It is forbidden for the listener to listen to backbiting and approve of it. He must denounce it if he is able to do so without apparent harm. Otherwise, he must denounce it with his heart and leave the gathering if he can. If he is compelled to remain in the gathering and is unable to denounce it, then he should remember Allah in his heart or with his tongue, or think about something else to distract himself from listening to the backbiting.