Exodus 13:11-16 - The Feast Of Unleavened Bread
11 And it shall be when Jehovah hath brought thee into the land of the Canaanites, as he hath sworn to thee and to thy fathers, and hath given it thee, 12 that thou shalt offer unto Jehovah all that breaketh open the womb, and every firstling that cometh of cattle which is thine: the males shall be Jehovah's. 13 And every firstling of an ass shalt thou ransom with a lamb; and if thou do not ransom it, thou shalt break its neck; and every firstborn of a man among thy sons shalt thou ransom.
14 And it shall be when thy son asketh thee in time to come, saying, What is this? that thou shalt say to him, With a powerful hand Jehovah brought us out from Egypt, out of the house of bondage. 15 And it came to pass, when Pharaoh stubbornly refused to let us go, that Jehovah slew all the firstborn in the land of Egypt, both the firstborn of men and the firstborn of cattle: therefore I sacrifice to Jehovah all that breaketh open the womb being males; and every firstborn of my children I ransom. 16 And it shall be for a sign on thy hand, and for frontlets between thine eyes, for with a powerful hand Jehovah brought us forth out of Egypt.