Numbers Chapter 3 Verse 13Because all the firstborn [are] mine; [for] on the day that I smote all the firstborn in the land of Egypt I hallowed unto me all the firstborn in Israel, both man and beast: mine shall they be: I [am] the LORD.

These [are] the names of the sons of Aaron, the priests which were anointed, whom he consecrated to minister in the priest's office.

And Nadab and Abihu died before the LORD, when they offered strange fire before the LORD, in the wilderness of Sinai, and they had no children: and Eleazar and Ithamar ministered in the priest's office in the sight of Aaron their father.

And the LORD spake unto Moses, saying,

Bring the tribe of Levi near, and present them before Aaron the priest, that they may minister unto him.

And they shall keep his charge, and the charge of the whole congregation before the tabernacle of the congregation, to do the service of the tabernacle.

And they shall keep all the instruments of the tabernacle of the congregation, and the charge of the children of Israel, to do the service of the tabernacle.

And thou shalt give the Levites unto Aaron and to his sons: they [are] wholly given unto him out of the children of Israel.

And thou shalt appoint Aaron and his sons, and they shall wait on their priest's office: and the stranger that cometh nigh shall be put to death.

And the LORD spake unto Moses, saying,

And I, behold, I have taken the Levites from among the children of Israel instead of all the firstborn that openeth the matrix among the children of Israel: therefore the Levites shall be mine;

And the LORD spake unto Moses in the wilderness of Sinai, saying,

Number the children of Levi after the house of their fathers, by their families: every male from a month old and upward shalt thou number them.

And Moses numbered them according to the word of the LORD, as he was commanded.

And these were the sons of Levi by their names; Gershon, and Kohath, and Merari.

And these [are] the names of the sons of Gershon by their families; Libni, and Shimei.

And the sons of Kohath by their families; Amram, and Izehar, Hebron, and Uzziel.

And the sons of Merari by their families; Mahli, and Mushi. These [are] the families of the Levites according to the house of their fathers.

Of Gershon [was] the family of the Libnites, and the family of the Shimites: these [are] the families of the Gershonites.

Those that were numbered of them, according to the number of all the males, from a month old and upward, [even] those that were numbered of them [were] seven thousand and five hundred.

The families of the Gershonites shall pitch behind the tabernacle westward.

The Book of Numbers, Chapter 3, Verse 13