Exodus 30:11-13

Then the LORD said to Moses, “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. Each 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.)