Numbers 18:14-16 New International Version - UK (NIVUK)
14 ‘Everything in Israel that is devoted[a] to the Lord is yours. 15 The first offspring of every womb, both human and animal, that is offered to the Lord is yours. But you must redeem every firstborn son and every firstborn male of unclean animals. 16 When they are a month old, you must redeem them at the redemption price set at five shekels[b] of silver, according to the sanctuary shekel, which weighs twenty gerahs.