Exodus 30:13-16

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. All who cross over, those twenty years old or more, are to give an offering to the LORD. The rich are not to give more than a half shekel and the poor are not to give less when you make the offering to the LORD to atone for your lives. Receive the atonement money from the Israelites and use it for the service of the tent of meeting. It will be a memorial for the Israelites before the LORD, making atonement for your lives.”