Ruling 1951

If a person gives someone zakat thinking that he is poor and later realises that he was not poor, or if on account of not knowing the ruling he gives zakat to someone whom he knows is not poor, it is not sufficient [and he will not have discharged his duty]. Therefore, in the event that the item he gave the beneficiary still exists, he must take it back from him and give it to someone entitled to receive zakat. However, if the item does not exist and the beneficiary knew it was given to him as zakat, then he can claim its replacement from the beneficiary and give it to someone entitled to receive zakat; but, if the beneficiary did not know it was zakat, he cannot take anything from him and he must give zakat again from his own property to someone entitled to receive it, even if, based on obligatory precaution, he investigated about the beneficiary or he relied upon something that was legally authoritative (al‑ḥujjah al‑sharʿiyyah) [such as the statement of a reliable person].