Numbers 18:15

18:15 The firstborn of every womb which they present to the Lord, whether human or animal, will be yours. Nevertheless, the firstborn sons you must redeem, and the firstborn males of unclean animals you must redeem.

Numbers 23:3

23:3 Balaam said to Balak, “Station yourself by your burnt offering, and I will go off; perhaps the Lord will come to meet me, and whatever he reveals to me I will tell you.” Then he went to a deserted height.