What is the ruling on a husband abandoning his father, mother, and sister, and preventing his wife and children from visiting or speaking with them, because his father insists on depositing his pension money in a usurious bank, and refuses all his son's attempts to convince him of the unlawfulness of that, and what is your advice in this situation?

Disobeying parents (ʿuqūq al-wālidayn) is one of the gravest major sins after associating partners with Allah, and it may be defined as a child harming one of their parents with something that would be considered a minor sin if directed towards others. Abandonment and estrangement are among the worst types of disobedience and the most sinful. It is not permissible for a son to abandon his parents, and he must immediately repent with remorse and cessation of the act, and promptly re-establish ties with them, even if his parents are polytheists. He should continue to advise his father with wisdom and good counsel regarding his interest-based money, while reminding him that an unlearned person who is excused might not be sinful if he emulates someone he trusts, and that for one who repents, "what has passed is his."