Exodus 30:12-14

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.)

14All who have reached their twentieth birthday must give this sacred offering to the Lord.