All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
We have already issued Fatwa 81725 clarifying that it is forbidden to celebrate birthdays, that this represents an act of imitating the non-Muslims and that it is not from the religion of Islam. We have also issued Fatwa 84942 clarifying that obedience to parents is only in what is not a disobedience to Allaah. Therefore, your husband should not have gone there as a way of obeying his parents or pleasing his relatives. However, if he went in order to deny what they would do, then this is permissible; rather, this would be one of the most important acts of obedience to Allaah as he went to fulfill a religious obligation, which is advising the Muslims. Indeed, the jurists mentioned that if a person is invited to a marriage banquet where there is evil and he is able to change the evil or to reduce it, then he is permitted to attend to achieve that benefit, but if he only knew about the evil once he attended and he could not change it, then he should leave.
Allaah Knows best.