What is the way to expiate the sin of a woman who bought a house with her husband’s money and her own money without his knowledge, and concealed that from him until he passed away, knowing that she did that to shelter her family?

A wife is not permitted to take her husband's money without his knowledge, unless he falls short in providing for her and their children. In such a case, she may take what is sufficient for her in a reasonable manner. The wife's actions of taking her husband's money without his permission are not permissible, as the Prophet, peace and blessings be upon him, said: "The property of a Muslim is not lawful except with his willing consent." Since she has repented, it is hoped that this is a true repentance. She must return the money to the heirs and firmly resolve not to repeat such an action.