Exodus 30:11-13

11Then the Lord said to Moses,

12“Whenever you take a census of the people of Israel, each man who is counted must pay a ransom for himself to the Lord. Then no plague will strike the people as you count them.

13Each person who is counted must give a small piece of silver as a sacred offering to the Lord. (This payment is half a shekel, based on the sanctuary shekel, which equals twenty gerahs.)