The scholars said concerning attending feast (event) and ceremonies during wedding and others :

If an invitee sees any reprehensible act in the event like drinking of alcohol, it is incumbent on him to condemn it for an Hadith was narrated by Muslim :

Whoever sees any reprehensible act should correct it with his hand, if he’s not capable, he should use his tongue (words), and if he is not capable, he should correct it with his heart, though that’s the weakest of faith

If they respond to him, he should remain there. If not, it is imperative for him to leave the event, and leaving (that event) demonstrates expression of displeasure with one’s heart. This rejection of the reprehensible act will humiliate the perpetrator. If one is seated with them, and he dislikes it, his sitting is therefore forbidden according to authentic view or opinion. 

If it is not possible for him to leave at night because he is afraid, or for any other reasonable excuse, he should sit, expressing his displeasure, without any sign indicating his satisfaction. [see. An-Nawawi’s Commentary on Sahih Muslim chapter 9, pages 234-236; Al -khatib’s Al Iqnaa’ commentary on Ibn Abu Shujaa’ Chapter 2, page 339].

Also, Abu Dahood narrated that the messenger of Allah, may Allah’s peace and blessings be upon him said: “When sin is done in the earth, he who sees it and disapproves of it will be taken like one who was not present, but he who is not present and approves of it will be like him who sees.”