Exodus 13:12

9 And it shall be for a sign to thee upon thy hand, and for a memorial between thy eyes; that the LORD'S law may be in thy mouth: for with a strong hand hath the LORD brought thee out of Egypt.

10 Thou shalt therefore keep this ordinance in its season from year to year.

11 And it shall be when the LORD shall bring thee into the land of the Canaanites, as he swore to thee and to thy fathers, and shall give it to thee,

12 That thou shall set apart to the LORD all that openeth the matrix; and every firstling that cometh of a beast which thou hast, the males [shall be] the LORD'S.

13 And every firstling of an ass thou shalt redeem with a lamb; and if thou wilt not redeem it, then thou shalt break his neck: and all the first-born of man among thy children shalt thou redeem.

14 And it shall be when thy son asketh thee in time to come, saying, What [is] this? that thou shalt say to him, By strength of hand the LORD brought us out from Egypt, from the house of bondage:

15 And it came to pass, when Pharaoh would hardly let us go, that the LORD slew all the first-born in the land of Egypt, both the first-born of man, and the first-born of beasts: therefore I sacrifice to the LORD all that openeth the matrix, being males; but all the first-born of my children I redeem.