Numbers 18:30-32

30Therefore thou shalt say unto them, When ye have heaved the best thereof from it, then it shall be counted unto the Levites as the increase of the threshingfloor, and as the increase of the winepress.1

31And ye shall eat it in every place, ye and your households: for it is your reward for your service in the tabernacle of the congregation.

32And ye shall bear no sin by reason of it, when ye have heaved from it the best of it: neither shall ye pollute the holy things of the children of Israel, lest ye die.