Kaffarah for deeming something lawful to be unlawful

Q: I proposed to marry a daughter of one of my relatives. However, some problems aroused that prevented the marriage; and as a result I took an oath that rendered all the daughters of this man (Part No. 23; Page No. 173) unlawful for me to marry and said that they were like my mother. Then, Allah (Exalted be He) willed that I marry one of them and now I have two children. After a period of time, some people said to me that I have to offer Kaffarah (expiation) of Zhihar (a man likening his wife to an unmarriageable relative), and that made me ask some shaykhs concerning this matter. They advised me to send my question to Your Eminence, bearing in mind that I read in the book "Al-Mughny", (volume seven, page 354), that according to Imam Ahmad a Kaffarah must be offered in my case.I hope you would give me a Fatwa (legal opinion issued by a qualified Muslim scholar) in this regard and the ruling concerning my children. I do not know whether I should stop my relation with my wife until I offer the Kaffarah, taking into consideration that this matter happened out of my ignorance. Please advise, may Allah reward you with the best!

A: You have to offer Kaffarah for an oath and make Tawbah (repentance to Allah) for what you did, because it is not permissible for a Muslim to declare as Haram (prohibited) what is made Halal (lawful) by Allah (Exalted be He). Furthermore, Kaffarah of Zhihar must be offered only in the case of declaring one's wife as unlawful. These women were not your wives at the time you took this oath.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.