My question as follows: My mother has been with my step-dad for 22 years. She is a Muslim and he claims to be a Christian, and I recently told her that it is unlawful for her to be married to him(they were married 12 yrs. ago). So can you please help me to give her a straight and clear answer to her situation. I want her to know the importance and seriousness of her situation, so Insha-Allah, that she will get out of it. References from Quran an Hadith would be most excellent!

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If the man whom your mother had married is Christian and is still so, and if he had not become Muslim before marrying your mother, then the latter committed a major sin by giving herself to a non-Muslim man. She is Muslim and believes in Allah and His Messengers while this man denies the existence of Prophet Muhammad as a Messenger and indeed of Islam and says that Allah, The Exalted, The One, is a third associate of two partners. How could she give such a person authority over her? She has obviously gone against the Orders of Allah, Who Says (what means): {And do not marry polytheistic men [to your women] until they believe. And a believing slave is better than a polytheist, even though he might please you. Those invite [you] to the Fire, but Allah invites to Paradise and to forgiveness, by His permission. And He makes clear His verses to the people that perhaps they may remember.} [Quran 2: 221]

She has also gone against the consensus of all Muslim scholars who are all agreed that it is prohibited for a Muslim woman to marry a non-Muslim man.

So, she must immediately separate from this man. If she has had children from this man, they are traced back to her, as it is a rule in the Sharee’ah that the children are traced back to the best of the two parents as far as religion is concerned. We ask Allah to guide this woman to the right path and return her back to the truth.

For more benefit that the marriage of a Muslim woman to a non-Muslim man is null and void, please refer to Fataawa 262615, 81220, 362398, and 393682.

Also, for more benefit on the religion of children when one of the parents is Muslim and another is not, please refer to Fataawa 81957, 86359, and 91184.

Allah knows best.