Topic: Maintaining Relations With a Muslim Son Living With a Non-Muslim Woman, and His Right to Inheritance

Since the woman in question has not accepted Islam, a valid Islamic marriage between her and the Muslim man has not taken place. Therefore, their living together as a couple and maintaining a marital relationship is forbidden and impermissible in Islamic law.
Allah says: *"And do not marry polytheist women until they believe."* (Al-Baqarah: 221)

*1) Maintaining or Cutting Ties*
In Islamic law, cutting ties with a fellow Muslim for more than three days without a valid reason is not permissible. However, when a person is openly committing a major sin and refuses to accept advice, it is permissible, and in some cases necessary, to temporarily boycott them or adopt a firm stance toward them as a means of correction and warning.
The following points should be kept in mind:
If the parents believe that firmness and a boycott are likely to make the son abandon this unlawful relationship, then adopting a strict stance is appropriate.
If, however, there is genuine concern that cutting ties completely may cause him to drift further away from the Deen, or even lead to apostasy, then maintaining limited contact with wisdom and care is permissible.
If contact is maintained, the sole purpose should be his correction, sincere advice, and wellbeing. No behaviour should be adopted that gives the impression of approving or accepting this unlawful relationship.
*2) Inheritance*
A Muslim committing a major sin does not leave the fold of Islam, as long as he has not committed clear-cut disbelief or apostasy. Therefore, if this person remains a Muslim in his beliefs, he will still be considered a Muslim despite his sinfulness. Accordingly, after the parents' death, he will be entitled to his full share of the inheritance just like the other heirs. He cannot be deprived of his inheritance merely on account of disobedience or sin. Islamic law does not give anyone the authority to disinherit a legal heir by declaring him disowned.
However, if the parents wish to distribute their wealth as gifts during their own lifetime, and out of this consideration wish to give this son a lesser amount as a form of warning, they may do so. But whatever remains of the estate after their death must be distributed among all legal heirs, including this son, according to their fixed shares. They cannot be deprived of what Islamic law has entitled them to.