Ruling on Attending a Wedding Feast Based on Shighar

Question:
Is it permissible for a Muslim to attend wedding celebrations if they are based on shighar—that is, exchange? And is it permissible for him to eat from that feast?

Answer:
If the marriage is shighar, it is not permissible for him to attend, nor to participate. Rather, he must denounce it and forbid it; because shighar marriage is not permissible.
Shighar marriage is when one says: "Marry me and I will marry you," and they condition the marriage on each other. This one marries this one’s daughter, or his sister, or marries his son, or his brother. It is called shighar marriage, which is equality and conditioning. Each one conditions the other to marry him, or to marry his son, or to marry his brother, and they contract for that. This is called shighar marriage, and it is invalid and not permissible absolutely, even if a mahr is named in it. So if you know that it is shighar, do not attend it. Rather, denounce them and say: "O my brothers, this is not permissible, and it is not lawful for you to do that." Do not attend them, and do not attend the feast either; because attending the feast is a type of approval of it.