Exodus 30:11-13 NIV

Then the LORD said to Moses, “When you take a census of the Israelites to count them, each one must pay the LORD a ransom for his life at the time he is counted. Then no plague will come on them when you number them. Each one who crosses over to those already counted is to give a half shekel, according to the sanctuary shekel, which weighs twenty gerahs. This half shekel is an offering to the LORD.