The Ruling on Marrying an Open Sinner and One Who Abandons Prayer

Question:
I have a sister, and my parents want to marry her to an open sinner. Should I prevent them from doing so?

Answer:
This requires detailed explanation. If the parents want to marry their daughter to an open sinner, and her brother does not approve of it, he should intervene in the matter in a good manner, without being rude to his parents. Instead, he should use kind words and say to them: "His character is such and such, and his character is such and such, and I fear for my sister regarding such and such." He should advise them and his sister about what he sees, but he should not use what is not befitting with his parents. This is because an open sinner is permitted to marry a woman who is not an open sinner (a chaste woman), provided he is not a disbeliever. She is allowed to marry him, and her parents are allowed to marry her to him if she consents to it, and there is no harm in this, even if he is not of equal status to her.
However, it is permissible for her to take him, and to marry him, just as it is permissible for a Qurayshi woman or a Tamimi woman to take a freed slave or a non-Arab, even if he is not of her lineage. This is because the most noble of people in the sight of Allah are the most righteous of them. So there is no harm in a non-Arab marrying an Arab woman, a Qurayshi woman, or a Hashimi woman. It is also permissible for a freed slave to marry one who is known by his tribe, such as a Qurayshi, a Tamimi, or the like. All of this is permissible, and the criterion is piety. (Al-Hujurat: 13)
But if the daughter is content with him, and her parents are content with him, and they fear that if they prevent it, she might fall into something greater, because some people may prevent a woman from something they think is better for her, but she might fall into corruption, she might fall into unlawful sexual intercourse, and that is greater. So one should look into this, and not be stubborn in opposing the parents, or the daughter, in a matter that is not forbidden.
As for if he does not pray, then there is no good in him, and he should not be married. But if he has other open sinfulness, he prays, he is a Muslim, but he may be afflicted with intoxicants, he may smoke, he may shave his beard, there may be other things he is criticized for, this does not prevent his marriage. But if another person is found who is better than him, that is better.
But today, the sound young man is few, the young man who is sound from these evils is few. So if the father wants not to marry her except to one who is perfect, with none of the defects, it may be difficult for him, and the daughter may remain with him for many long years, and perhaps she will remain until the end of time. So he should look into that, and choose for her one who is less evil, and one who is less afflicted, and perhaps Allah will guide him afterwards through advice and direction.
As for the disbeliever, no, it is not permissible for her to marry a disbeliever who does not pray, or who is known for cursing the religion, or who is known for licentiousness. This is not permissible, neither for her nor for her parents.