Numbers 18:14-17

¹⁴Everything in Israel that is set apart to belong to me also belongs to you.

¹⁵The firstborn males, both humans and domestic animals, that are offered to me, will be yours. But people must buy back their firstborn sons and the firstborn animals that may not be used for sacrifices.

¹⁶They must buy them back when they are one month old. The price that they must pay for each one is five pieces of silver. They must weigh the silver on the scales that are in the Sacred Tent.

¹⁷But they are not permitted to buy back the firstborn cattle or sheep or goats. They are holy and have been set apart for me. Slaughter them and sprinkle their blood on the altar. Then completely burn the fat of those animals on the altar to be an offering to me. The smell as they burn will be very pleasing to me.