A family with 4 children: the man gives each week 100 euros to his wife to spend as she likes. After some time, she has 1500 euros. Her husband keeps asking her again and again how much money she has now. She refuses to tell him about the 1500 euros. She does not work and does not have any income other than what her husband gives her. What does Allah or the Prophet $Mohammed$$ (Sallallahu Alaihi wa Sallam) say about this?

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

Spending on one's wife and children is an obligation upon the capable husband according to his capability.

Hind bint ‘Utbah said to the Prophet : “O Messenger of Allah! Abu Sufyan is a miser and he does not give me what is sufficient for me and my children. Can I take of his property without his knowledge?” The Prophet said, “Take what is sufficient for you and your children according to what is just and reasonable.” [Al-Bukhari and Muslim]

If a husband gives a certain amount to his wife and makes her the owner of that amount or allots her a certain amount, according to the customs in that place, for the expenditure of the home, then she becomes the owner of that amount. So, she can act freely in the amount that remains after fulfilling the expenditure of the home. Indeed, any action that could harm her body or prevent her husband from enjoying sex with her is forbidden. [You may refer to Kashshaaf Al-Qinaa’ written by Al-Buhooti]

On the other hand, if the husband gives her only to spend on herself and children, and he will give her more if the given amount is not sufficient for the expenditures, then, in this case, she does not own the amount and therefore she should not spend other than that in the expenditure of the home, and also she should not hide the remaining amount. The ruling does not change even if the woman works and gets a salary.

Allah knows best.