Exodus 34:18-20

18“You must celebrate the Festival of Unleavened Bread. As I commanded you, you must eat unleavened bread for seven days at the appointed time in the month of Abib, because in that month you came out of Egypt.

19“Every first male offspring is mine, even the firstborn males of all your livestock, whether cattle, sheep, or goats.

20It will cost you a sheep or a goat to buy back the firstborn donkey. If you don’t buy it back, then you must break the donkey’s neck. You must buy back every firstborn of your sons. “No one may come into my presence without an offering.