What is the ruling on da'wah (inviting to Islam) and preaching in "impure" places such as nightclubs?

Calling to Allah in places where sins are committed depends on weighing the benefits against the harms. If the benefits outweigh the harms, then it is permissible; otherwise, it is not. The ruling varies according to the place, time, and individual. It is not appropriate to call a drunkard while he is in a state of intoxication. However, one may call someone who is not drunk or has sobered up, if it is highly probable that he will benefit. It is better to wait for frequenters outside these places to call them before they enter; for preventing entry is easier than dealing with the sin after it has occurred.