Exodus 30:11-13

And Jehovah spake unto Moses, saying, When thou takest the sum of the children of Israel, according to those that are numbered of them, then shall they give every man a ransom for his soul unto Jehovah, when thou numberest them; that there be no plague among them, when thou numberest them. This they shall give, every one that passeth over unto them that are numbered, half a shekel after the shekel of the sanctuary; (the shekel is twenty gerahs), half a shekel for an offering to Jehovah.