Numbers 3:44-47

44And Jehovah spoke to Moses, saying,

45Take the Levites instead of all the firstborn among the children of Israel, and the cattle of the Levites instead of their cattle; and the Levites shall be mine: I am Jehovah.

46And for those that are to be ransomed, the two hundred and seventy-three of the firstborn of the children of Israel, which are in excess over the Levites,

47thou shalt take five shekels apiece by the poll, according to the shekel of the sanctuary shalt thou take them, — twenty gerahs the shekel;