3,679. Redeeming the Firstborn Early

Hilchos Bikkurim 11:18

Regarding one who redeems his son within thirty days of birth: If he tells the kohein that he’s redeeming the son then, the redemption is ineffective. If he tells the kohein that the redemption should take effect after thirty days, the son is redeemed. This is so even if the coins no longer exist after thirty days.

Hilchos Bikkurim 11:19

If there’s a doubt as to whether or not a son must be redeemed, he is exempt. This is because of the rule that the burden of proof is on the one who wants to take property from another (i.e., the kohein must prove that the child is obligated in pidyon haben). If a father dies within thirty days of the son’s birth, we assume that the baby wasn’t redeemed unless the father left proof that he redeemed him. If the father died more than thirty days after the son’s birth, we assume that the baby was redeemed unless the father made a dying statement that such is not the case.