Bamidbar 3:13-15

Orthodox Jewish Bible

¹³ Because all the bechor are Mine; for on the yom that I struck down all the bechor in Eretz Mitzrayim I set apart as kodesh unto Me all the bechor in Yisroel, both man and beast: Mine shall they be: I am Hashem.

¹⁴ And Hashem spoke unto Moshe in the midbar of Sinai, saying,

¹⁵ Count the Bnei Levi by the bais of their avot, by their mishpekhot; every zachar from a month old and upward shalt thou number them.