Is it permissible to visit a Muslim sister married to a non-Muslim, knowing that the sister's husband is not present and that the husband objects to this visit?

Upholding kinship ties (Silat al-Rahim) is obligatory for a woman, and her husband is not permitted to prevent her from doing so. If he forbids her from visiting but allows her to greet them or send gifts, then she should do that. If he forbids her from all forms of maintaining ties, then there is no obedience to a creature in disobedience to the Creator. She should maintain her kinship ties in a way that minimizes the husband's displeasure, such as by sending a gift or a greeting, and she should conceal it if she fears negative repercussions. If they are in dire need, she should maintain ties with them as necessitated by their need, even if her husband forbids her. She should maintain kinship ties by offering condolences during calamities and congratulations during joyous occasions, while adhering to the Sharia-compliant guidelines regarding dress and speech.