What must be done after taking Zakat money from a brother out of ignorance of the ruling, and buying some items with it, such as computer parts and a monitor, and is it obligatory to give a certain amount in charity or to dispose of these items, knowing that the current money is not enough to buy replacements for them?

Allah Almighty has clarified those eligible for Zakat in His saying: "Indeed, Sadaqat (Zakat) are only for the poor and the needy and those employed to collect [Zakat] and those whose hearts are to be reconciled and for freeing captives and for those in debt and for the cause of Allah and for the traveler – an obligation [imposed] by Allah. And Allah is Knowing and Wise."

If you are poor and do not find enough for your basic needs, then it is permissible for you to take from Zakat, and it is permissible for your brother to give his Zakat to you, because your maintenance is not obligatory upon him. Rather, you are more deserving of his Zakat, based on the saying of the Prophet, peace and blessings be upon him: "Charity given to a poor person is one charity, but charity given to a relative is two: charity and maintaining ties of kinship." And if you take Zakat while you are poor, it is permissible for you to buy whatever permissible things you desire, even for entertainment.

However, if you are not poor, nor in debt, nor eligible under any of the descriptions mentioned in the verse, then it is not permissible for you to take from Zakat. And if you have taken, you must repent and return what you took to your brother, because it is unlawful wealth for you. It is not sufficient to give a part of it in charity; rather, you must return the amount taken to its owners. The unlawfulness of this wealth is attached to your liability, but the goods you bought with it can be used after returning the equivalent amount or seeking your brothers' forgiveness for it.