Is it permissible to marry a girl whose father deals in usury? What is the ruling on accepting what he pays for her preparation? Is refusing to marry her considered an injustice? And how is the result of the Istikhara prayer known?

The fact that the girl's father deposited his money in usurious banks is not a barrier to proposing to his daughter and marrying her, as long as she possesses good character and religious devotion. This is because she embodies what the Prophet, peace and blessings be upon him, advised when he said: "Seek the one who is religious, and you will prosper." There is no consideration for her father being involved in these sins and Sharia violations, due to the Almighty's saying: "Every person, for what he earned, is retained," and "No bearer of burdens will bear the burden of another."

If all his earnings are from the proceeds of usurious banks, then there is no benefit in what he spends on equipping her, because it is unlawful wealth that is not permissible to benefit from by choice. However, if most of it is from usury, with a portion of lawful money, then using this dowry becomes disliked (makrooh). The general rule is that it is not permissible to deal with someone whose entire wealth is unlawful, nor to eat from his money. As for someone whose majority of wealth is unlawful, the preponderant opinion is that both eating from his money and dealing with him are disliked, unless it is known that he purchased the specific food with unlawful money.

You have the right not to accept the girl as a wife, just as she has the right to accept or reject a specific husband. As for the result of Istikhara (guidance prayer), it is the facilitation of the matter. One should not rely heavily on a feeling of openness or constriction in the chest thereafter. If the action is facilitated for you after Istikhara, it will only be good for you.