Numbers 1:17-19

17 And Mosheh and Aharon took these men who were called by name,

18 and they assembled all the congregation together on the first day of the second new moon. And they declared their ancestry by clans, by their fathers’ houses, according to the number of names, from twenty years old and above, each one head by head.

19 As יהוה commanded Mosheh, so he registered them in the Wilderness of Sinai.