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.
It is an obligation to pay Zakah on the money that are common between the spouses according to the individual share of each one of them if this share reaches the Nisaab (i.e. the minimum amount liable for Zakat) and a whole lunar year elapses on it. The husband should look at his share from that money if a whole lunar year elapses on it and if it reaches the Nisaab even by adding it to his other money or tradable items on which a whole lunar year elapsed, then he should pay the Zakah on it but he should not pay the Zakah on the money of his wife without her permission.
Similarly, the wife should look to her share from the money, and if it reaches the Nisaab and a whole lunar year elapses on it, even if it reaches the Nisaab by including the money that she hides from her husband, then she should pay the Zakah on it and she may deputize her husband to pay the Zakah on the money that is mixed between them.
However, it is not an obligation on the husband and wife to pay their Zakah together; rather, each one of them is obliged to pay his/her own Zakah on his/her own money. Each one is obliged to pay his/her own Zakah and he/she has nothing to do with the Zakah of the other, unless if one wants to advise or guide the other but they are not obliged to pay the Zakah together; for more benefit, please refer to Fatwa 102345.
Moreover, the wife has an independent financial liability and if she has money to hide from her husband and it fulfils the conditions of Nisaab, then she is obliged to pay Zakah on it and it is not a condition for her to tell her husband about it.
For more benefit, please refer to Fatwa 95631.