Pidyon Haben

Lifecycle

Pidyon HaBen ("redemption of the son") is a ceremony in which a 30-day old firstborn son is redeemed by transferring monetary objects to a kohen. The commandment is rooted in Exodus 13:12-15, which ties the practice to the Exodus story and God's sparing of Israelite firstborns when Egyptian firstborns were killed, and Numbers 18:15-16.

Sources

והיה כי ישאלך בנך, "It will be when your son enquires of you, etc." The Torah means that when your son observes you perform the ceremony of redeeming a firstborn he will ask you the reason for that commandment. In that event you are obligated to explain the meaning of the commandment. If the son does not ask you, you are not obligated to answer him except on the night of the Passover. This is the reason the Torah added the word מחר, "tomorrow…

Or HaChaim on Exodus 13:14:1

also, the first-born of our sons and our beasts, as is written in the Teaching; and to bring the firstlings of our cattle and flocks to the House of our God for the priests who minister in the House of our God.

Nehemiah 10:37

“And when יהוה has brought you into the land of the Canaanites, as [God] swore to you and to your fathers, and has given it to you, you shall set apart for יהוה every first issue of the womb: every male firstling that your cattle drop shall be יהוה’s. But every firstling ass you shall redeem with a sheep; if you do not redeem it, you must break its neck. And you must redeem every male first-born among your children. And when, in time to come, a child of yours asks you, saying, ‘What does this mean?’ you shall reply, ‘It was with a mighty hand that יהוה brought us out from Egypt…

Exodus 13:11-16

“Consecrate to Me every male first-born; human and beast, the first [male] issue of every womb among the Israelites is Mine.”

Exodus 13:2

And when, in time to come, a child of yours asks you, saying, ‘What does this mean?’ you shall reply, ‘It was with a mighty hand that יהוה brought us out from Egypt, the house of bondage. When Pharaoh stubbornly refused to let us go, יהוה slew every [male] first-born in the land of Egypt, the first-born of both human and beast. Therefore I sacrifice to יהוה every first male issue of the womb, but redeem every male first-born among my children.’

Exodus 13:14-15

The first [male] issue of the womb of every being, human or beast, that is offered to יהוה, shall be yours; but you shall have the male first-born of human beings redeemed, and you shall also have the firstling of impure animals redeemed. Take as their redemption price, from the age of one month up, the money equivalent of five shekels by the sanctuary weight, which is twenty gerahs.