Exodus 13:13-14

A firstborn donkey may be bought back from the LORD by presenting a lamb or young goat in its place. But if you do not buy it back, you must break its neck. However, you must buy back every firstborn son. “And in the future, your children will ask you, ‘What does all this mean?’ Then you will tell them, ‘With the power of his mighty hand, the LORD brought us out of Egypt, the place of our slavery.