Exodus 30:11-13

The LORD also spoke to Moses, saying, “When you take a census of the sons of Israel to number them, then each one of them shall give a ransom for himself to the LORD, when you number them, so that there will be no plague among them when you number them. This is what everyone who is numbered shall give: half a shekel according to the shekel of the sanctuary (the shekel is twenty gerahs), half a shekel as a contribution to the LORD.