Is a marriage contracted without the knowledge or approval of the bride's guardian Islamically valid, and what advice should be given to the husband in this situation?

Marriage is not valid except with a guardian, due to the saying of the Messenger of Allah, peace and blessings be upon him: "There is no marriage except with a guardian," and "Any woman who marries without the permission of her guardian, her marriage is void." The most deserving person to give a woman in marriage is her father, then the closest of her male agnates ( asabat ), and so on. If the guardianship of the closest one is forfeited, then the next in line among them gives her in marriage. If the guardianship of all of them is forfeited, then the ruler is the one who gives her in marriage, and the judge acts in his stead. If the father of the girl has lost his uprightness ( adalat ), he has no guardianship. If she has another righteous guardian besides him, then her marriage is not valid except through him. But if she has no righteous guardian other than him, and the Muslim community deems it beneficial for her to marry a compatible man ( kuf’ ), then there is no harm in this marriage. It is obligatory for whoever wishes to marry to choose a righteous and religious wife.