Exodus 13:11-16 - The Feast Of Unleavened Bread
11 And it shall be, when LORD shall bring thee into the land of the Canaanite, as he swore to thee and to thy fathers, and shall give it to thee, 12 that thou shall set apart to LORD all that opens the womb. And every firstling which thou have that comes of a beast, the males shall be LORD's. 13 And every firstling of a donkey thou shall redeem with a lamb, and if thou will not redeem it, then thou shall break its neck. And all the first-born of man among thy sons thou shall redeem.
14 And it shall be, when thy son asks thee in time to come, saying, What is this? that thou shall say to him, By strength of hand 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 LORD slew all the first-born in the land of Egypt, both the first-born of man, and the first-born of beast. Therefore I sacrifice to LORD all that opens the womb, being 16 And it shall be for a sign upon thy hand, and for frontlets between thine eyes, for by strength of hand LORD brought us forth out of Egypt.