Liturgy do Liczb 18:37

This, my first born son, is the first issue of his mother's womb, and the Holy One, blessed is He has commanded to redeem him, as it is said: And those that are to be redeemed of them, from a month old shall you redeem them, according to your estimation, for the money of five silver shekalim, of the shekel of the Sanctuary which is equal to twenty geirah.¹Numbers 18:16. And it is said: Sanctify unto me all the firstborn, whatsoever opens the womb among the Children of Israel, both of man and of beast is Mine.²Exodus 13:2.

which is equal to twenty geirah.¹Numbers 18:16.