How do I deal with colleagues who engage in bribery?

You must denounce bribery to your colleagues and advise them against it, for bribery is one of the gravest sins and transgressions. The Messenger of Allah (peace and blessings be upon him) cursed the briber, the bribed, and the intermediary between them. The legal purpose of denouncing evil is to change it, and this should be done with wise methods that observe the guidelines for denouncing evil. These include: combining encouragement towards lawful earnings with warning against unlawful ones, gradualism in methods, understanding the nature of the prohibition and its proofs, knowing the ways to combat those who take bribes, and praying for their guidance. If you fear for your faith due to associating with them, then separation from them is required, along with denouncing their actions, for a person is upon the religion of his friend.