Reference to Fatwa: 89467 recently. I now understand that my marriage to a woman who is neither a practicing Christian or Jew is invalid and I have to be separated from her. My only question to you is to kindly tell me about the following:
If I leave her I have to leave my son born out of this marriage here in Europe and I am not in a position to take custody of my son either legally or on mutual understanding through discussion. I have to leave him here and then he will not be raised a Muslim. Please tell me is this sin going to be on my side if he is not going to be a believer due to these circumstances? I know I have to leave her and my son with her. I am completely helpless in taking his custody. May Allaah forgive me for all what I have done so far only because of my ignorance of Islamic Laws.

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 ask Allaah to exalt his mention as well as that of his family and all his companions.

First we confirm what we have mentioned in the previous Fatwa, that your marriage with this woman who was neither a Christian nor a Jew is invalid. You have to separate from her (and stop sleeping with her), however, your child is traced back to you as long as you married her assuming that the marriage with her was correct.

This woman has no right to foster the child because she is not a Muslim and is not from the people of the book. Religiously, you have the right in fostering your child, so you have to endeavour to find a way to take the child from his mother. If this has been made easy, then, all perfect praise be to Allaah, otherwise you can agree with her to visit him from time to time while advising and guiding him, and clarifying to him the Islamic creed and its excellence. Additionally, you have to do your best to treat him kindly so that he would love you and will be attracted to be raised on Islam principles and accept your advice until he reaches the time he would be independent from his mother. If you are unable to take your son away from her, or unable to visit him after doing your best, then we hope you are not sinful, as Allaah does not burden a soul more than it could bear.

Finally, it should be noted that a Muslim should not act before knowing the religious ruling about the matter in order to avoid unpleasant consequences, due to negligence in asking the scholars. 

Allaah knows best.