Intention (niyyat) when paying Zakat
Q: Is it important to have an intention when giving Zakat, just as we make an intention before praying (salah)?
A: As Zakat is an act of worship, to have an intention is a condition of its validity. The majority of scholars from the four schools of jurisprudence are in agreement on this matter. The intention must be there at the time of paying the Zakat.
According to the Hanafis, Malikis, and Shafiis the intention can also be made at the time of setting money aside for the payment of Zakat.
There is nothing specific to say when making this intention. It suffices to merely have the thought in your mind.
If a person makes a donation without having the intention for Zakat, then this donation will not be counted as Zakat. If later they make the intention for this donation to count towards their Zakat, it will still not be valid. The liability of the Zakat will remain until they make the donation again with the Zakat intention.
Q: My father isn’t practising and has never paid Zakat. Can I pay Zakat on his behalf?
A: The Zakat paid on behalf of a sane adult will not be valid if it has been paid without their permission.
As explained above, for the Zakat to be valid, there must be an intention from the payer which clearly isn’t the case in your situation, unless you seek your father’s permission.
There is no disagreement on this issue between any of the four schools of jurisprudence.