BaMidbar (Numbers) 18:21-32
21“To the sons of Levi, Behold! I have given every tithe in Yisra’el as a heritage in exchange for the service that they perform, the service of the Tent of Meeting – 22so that the Children of Yisra’el shall not again approach the Tent of Meeting to bear a sin to die. 23The Levi’im himself shall perform the service of the Tent of Meting, and they shall bear their iniquity, an eternal decree for your generations; and among the Children of Yisra’el the shall not inherit a heritage. 24For the tithe of the Children of Yisra’el that they raise up to HaShem as a gift have I given to the Levi’im as a heritage; therefore have I said to them: Among the Children of Yisra’el they shall not inherit a heritage.”
25HaShem spoke to Moshe, saying, 26” To the Levi’im shall you speak and you shall say to them: When you accept from the Children of Yisra’el the tithe that I have given you from them as your heritage, you shall raise up from it a gift to HaShem, a tithe from the tithe. 27Your gift shall be reckoned for you like grain from the threshing-floor and like ripeness of the vat. 28So shall you, too, raise up the gift of HaShem from all you tithes that you accept from the Children of Yisra’el, and you shall give from it a gift of HaShem to Aharon the Kohen. 29From all your gifts you shall raise up every gift of HaShem, from all its best part, its sacred part from it.
30“You shall say to them: ‘When you have raised up its best from it, it shall be considered for the Levi’im like the produce of the threshing-floor and the produce of the vat. 31You may eat it everywhere, you and your household, for it is a wage for you in exchange for your service in the Tent of Meeting. 32You shall not bear a sin because of it when you raise up its best from it; and the sanctities of the Children of Yisra’el you shall not desecrate, so that you shall not die.’”