הלכה על במדבר 18:24

The commandment of the first tithe: That the Children of Israel were obligated to give one tenth part of the seed of the land to the Levites, as is is stated (Numbers 18:24), "For it is the tithes of the Children of Israel that they will give to the Lord that I give to the Levites as a gift." And it is stated in the Order of Eem Bechukotai (Leviticus 27:30), "And all of the tithe of the land, etc. it is for the Lord." And that is what is called the first tithe (maaser rishon).