Question 4: What is the ruling of Islam regarding a brother whose sister is about to hold a wedding in which musical instruments will be used and other matters contradicting the teachings of Allaah and His Messenger. Should her brother attend the wedding or not? If he can save himself from the Fitnah (temptation) by staying in his room, is it permissible for him to remain at home? What should he do if his father asks him to do some things related to the wedding?
Answer: If this young man can assist in reducing the Fitnah in his sister’s wedding, there is nothing wrong with his presence for the benefit of resisting evil. However, if he finds this difficult, he should not attend the wedding so as not to cooperate in or courage the evil. There is nothing wrong with his bringing some things that his father may require as long as they are permissible, not involving any disobedience to Allaah… read more here.