Numbers 18:27 WEB

²⁵  Yahweh spoke to Moses, saying,

²⁶  Moreover you shall speak to the Levites, and tell them, When you take of the children of Israel the tithe which I have given you from them for your inheritance, then you shall offer up a heave-offering of it for Yahweh, a tithe of the tithe.

²⁷  Your heave-offering shall be reckoned to you, as though it were the grain of the threshing floor, and as the fullness of the winepress.

²⁸  Thus you also shall offer a heave-offering to Yahweh of all your tithes, which you receive of the children of Israel; and of it you shall give Yahweh's heave-offering to Aaron the priest.

²⁹  Out of all your gifts you shall offer every heave-offering of Yahweh, of all the best of it, even the holy part of it out of it.