Exodus 30:11-15

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.) All who have reached their twentieth birthday must give this sacred offering to the LORD. When this offering is given to the LORD to purify your lives, making you right with him, the rich must not give more than the specified amount, and the poor must not give less.