Assalaamu alaykum. I would like to know the following: does a man have to inform the first wife if he marries a second? What if he does not inform her or denies having a second wife (while he does have one) and then dies, and suddenly the second wife appears at the funeral? Or what if, without their knowledge that they are siblings, the children fall in love with each other?Please advise. Wassalaam.

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

The husband is not obliged to inform his first wife that he is married to a second wife, but it is more appropriate that he does not conceal this fact from her, especially if he fears that not informing her would lead to disputes, conflicts, or something forbidden. Please refer to fataawa 82068 and 86395 with respect to the first part of your question.

The answer to the second part of your question is that ignorance is one of the impediments that do not render a person accountable in general. So if a person does something that violates the sharee'ah out of ignorance and not knowing that it is forbidden, then he is not held accountable for it.

Shaykh Ibn ‘Uthaymeen said, “There are some impediments for rendering someone accountable, among which are: ignorance, forgetfulness, and coercion; because the Prophet said, 'Allaah has forgiven my nation for things they forget, do by mistake, or are forced to do.' [Ibn Maajah and Al-Bayhaqi]. There is evidence from the Quran and Sunnah that indicates its authenticity. Ignorance means lack of knowledge, so if an adult person does something forbidden out of ignorance of the fact that it is forbidden, then there is no sin on him.”

Allaah knows best.