What is the ruling on dealing with a person who claims knowledge of the unseen, uses "putrid incense," water, and salt for healing, and threatens whoever does not believe him, and how can one protect oneself and convince her husband not to follow him?

Marital afflictions do not necessarily stem from sins or magic; they might be a test ( ابتلاء ), for the prophets are the most severely tested among people. If it is highly probable that the afflictions are due to magic, then the treatment is through ruqyah (Islamic exorcism) by reciting the Qur’an, adhkar (remembrances), and supplications. It is preferable for a Muslim to perform ruqyah on themselves, but if they need someone else to perform it, they should seek out people of integrity and beware of magicians and soothsayers. One can protect themselves from magic by frequently remembering Allah, reciting the Qur’an, and consistently observing the morning and evening adhkar. It is also important to frequently supplicate for the husband's repentance and guidance, advise him in the best manner, and seek help from his close relatives who are righteous.