Leviticus 27:30-33 GNT
 One tenth of all the produce of the land, whether grain or fruit, belongs to the LORD.  If you wish to buy any of it back, you must pay the standard price plus an additional 20 percent.  One of every ten domestic animals belongs to the LORD. When the animals are counted, every tenth one belongs to the LORD.  You may not arrange the animals so that the poor animals are chosen, and you may not make any substitutions. If you do substitute one animal for another, then both animals will belong to the LORD and may not be bought back.
I know of two men who started business with this view: "We will give to God one-tenth of our profits." The first year the profits were considerable; the tithe was consequently considerable. The next year there was increase in the profits, and, of course, increase in the tithe. In a few years the profits became very, very large indeed, so that the partners said one to another: "Is not a tenth of this rather too much to give away? Suppose we say we will give a twentieth?" And they gave a twentieth; and the next year the profits had fallen down; the year after they fell down again, and the men said to one another, as Christians should say in such a case, "Have not we broken our vow? Have we not robbed God?" And in no spirit of selfish calculation, but with humility of soul, self-reproach and bitter contrition they went back to God and told Him how the matter stood, prayed His forgiveness, renewed their vow, and God opened the windows of heaven and gave back to them all the old prosperity.
(Joseph Parker, D. D.)