Alms Tax: Non-Liability of an Unaware Poor Person for Zakat Given Prematurely
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1985
If a poor person does not know that zakat has not become obligatory for someone and he accepts something from him as zakat and it perishes while it is with him, he [the poor person] is not responsible for it; and the person who gave the thing cannot count it as zakat.
-Ayatullah Sistani, Practical Laws of Islam, Alms Tax (Zakat)