Numbers 18:21-31

21 And, behold, I have given to the sons of Levi every tithe in Israel for an inheritance for their services, whereinsoever they perform ministry in the tabernacle of witness.
22 And the children of Israel shall no more draw nigh to the tabernacle of witness to incur fatal guilt.
23 And the Levite himself shall perform the service of the tabernacle of witness; and they shall bear their iniquities, it is a perpetual statute throughout their generations; and in the midst of the children of Israel they shall not receive an inheritance.
24 Because I have given as a distinct portion to the Levites for an inheritance the tithes of the children of Israel, whatsoever they shall offer to the Lord; therefore I said to them, In the midst of the children of Israel they shall have no inheritance.
25 And the Lord spoke to Moses, saying,
26 Thou shalt also speak to the Levites, and shalt say to them, If ye take the tithe from the children of Israel, which I have given you from them for an inheritance, then shall ye separate from it a heave-offering to the Lord, a tenth of the tenth.
27 And your heave-offerings shall be reckoned to you as corn from the floor, and an offering from the wine-press.
28 So shall ye also separate them from all the offerings of the Lord out of all your tithes, whatsoever ye shall receive from the children of Israel; and ye shall give of them an offering to the Lord to Aaron the priest.
29 Of all your gifts ye shall offer an offering to the Lord, and of every first-fruit the consecrated part from it.
30 And thou shalt say to them, When ye shall offer the first-fruits from it, then shall it be reckoned to the Levites as produce from the threshing-floor, and as produce from the wine-press.
31 And ye shall eat it in any place, ye and your families; for this is your reward for your services in the tabernacle of witness.

The Brenton translation of the Septuagint is in the public domain.