Is an expiatory oath (kaffarat yamin) incumbent upon me after having sexual intercourse with my wife due to ignorance of the ruling?

If what was uttered was an oath and the questioner broke it by having intercourse with his wife, then there is no blame upon him for breaking the oath before performing the expiation for the oath. This expiation is feeding ten poor people, or clothing them, or freeing a slave. If he cannot find any of these, then it is fasting for three days.

However, if it was Dhihar, then it is not permissible for him to approach his wife until after performing the expiation for Dhihar. This expiation is freeing a slave before they touch each other. If he cannot find one, then it is fasting for two consecutive months before they touch each other. If he is unable to do that, then it is feeding sixty poor people.

He must repent and seek forgiveness, and not have intercourse with his wife until he performs the expiation for Dhihar.