How to interact with sister living with non-Muslim man and their daughter?

Wa ‘Alaykumussalaam wa Rahmatullaahi wa Barakaatuh.

1) Of course, the Nikaah is invalid, and living with the non-muslim is equivalent to Zina.

Please refer to the following link for substantiation on this matter:

http://www.cislamonline.com/qa.php?id=2394

However, the situation seems to be out of your control. The most you can do to help your sister is to advise her. If you terminate all contact with her, you will be unable to do even that much. Living with a non-Muslim man already has taken her away from Islamic surroundings and practices. If her own Muslim family disown her, she will be driven farther away from Deen, and then the possibilities of her adopting Islamic values, and implementing the same in her child’s life, will be awfully slim.

Do not for a moment, let her feel that it is fine for her to be living the way she is, but in gentle and compassionate ways, explain to her the importance of leading an Islamic lifestyle. Islam is a religion that has been spread through the beautiful character of those who upheld it, starting with the Prophet (sallallaahu ‘alayhi wa sallam) and his companions (may Allaah be pleased with them). Who knows, your good character towards your sister, her child, and the man she is living with, may result in all of them recognising the beauty of Islam. On the other hand, if you are hostile towards them, they will be daunted and discouraged, and in your sister’s case, it will increase her in rebellion.

2) With regard to helping her, we can say that if by helping you mean assistance and support that will encourage her to continue this or any other form of sin, then this is prohibitted in Islam.

Allaah Most High says in the Noble Qur’aan

“Help you one another in Al-Birr and At-Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allaah. Verily, Allaah is Severe in punishment.” (al-Maa-idah, 5:2)

And Allaah knows best.

Wassalaam.

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A. Z. Pandor