Exodus 30:11-13

11Then the Lord said to Moses,

12“When you take the census of the Israelites, each one shall give a ransom for himself to the Lord when you count them, so that no plague will come on them when you number them.

13This is what everyone who is counted shall give [as he joins those already counted]: a half shekel, according to the sanctuary shekel (the shekel is twenty gerahs); a half shekel as a contribution to the Lord.