Numbers 18:15-18

¹⁵Every first issue of the womb of all flesh, whether man or animal, which they offer to the Lord, shall be yours; nevertheless the firstborn of man you shall surely redeem, and the firstborn of unclean animals you shall redeem. ¹⁶As to their redemption price, from a month old you shall redeem them, by your valuation, five shekels in silver, according to the shekel of the sanctuary, which is twenty gerahs. ¹⁷But the firstborn of an ox or the firstborn of a sheep or the firstborn of a goat, you shall not redeem; they are holy. You shall sprinkle their blood on the altar and shall offer up their fat in smoke as an offering by fire, for a soothing aroma to the Lord. ¹⁸Their meat shall be yours; it shall be yours like the breast of a wave offering and like the right thigh.