Bamidbar 1:18-20

Orthodox Jewish Bible

¹⁸ And they assembled kol HaEdah together on the first yom of the second month, and they declared their family after their mishpekhot, by the bais of their avot, according to the number of the shmot, from twenty years old and upward, one by one.

¹⁹ As Hashem commanded Moshe, so he counted them in the midbar of Sinai.

²⁰ And the bnei Reuven, Yisroel’s bechor, by their toldot, after their mishpekhot, by the bais of their avot, according to the number of the shmot, one by one, every zakhar from twenty years old and upward, all that are ablebodied to serve in tzava;