OT § 181

The Lord spoke to Moses on the day on which he brought the children of Israel out of the land of Egypt, saying, ‘Sanctify to me every first-born, first produced that opens every womb among the children of Israel’. And Moses said to the people, ‘Remember this day, on which you came out of Egypt, from the house of slavery, for the Lord has brought you out from there with a mighty hand. And keep his law. And it shall be that when the Lord God brings you into the land of the Chananites, in the way that he swore to your fathers, you shall set apart everything that opens the womb; the males to the Lord. But if after this your son asks you, saying, “What is this?”, you will say to him, “God brought us out of Egypt, from the house of slavery, with a mighty hand. And when Pharao hardened his heart against sending us out, the Lord slew every first-born in the land of Egypt, from the first-born of humans to the first-born of animals. This is why I sacrifice everything that opens the womb; the males to the Lord, and every first-born of my sons I will redeem”. And it will be for a sign upon your hand, and immovable before your eyes, because thus said the Lord the Almighty, “All the first-born of your sons you will give me. And it shall be that everyone who gives birth to a male child shall circumcise the flesh of its foreskin on the eighth day. And for thirty three days he will not come into the sanctuary of God to the Priest, until the days of purification are completed. And after this he will offer an unblemished yearling lamb to the Lord for a holocaust, and a young pigeon or turtle dove to the Priest at the door of the Tabernacle of Witness. Or instead of these he will offer two young pigeons or two turtle doves. And the Priest will make atonement for him. Because these have been offered to me as an offering out of all the children of Israel. And I have taken them and sanctified them for myself in place of the first-born of the Egyptians, on the day when I smote every first-born in the land of Egypt from human to beast of burden,” said God the Most High, the Holy One of Israel.’