Genesis 47:23-26

23Then Joseph said to the people, “Look, today I have bought you and your land for Pharaoh; now, here is seed for you, and you shall plant the land.

24At harvest time [when you reap the increase] you shall give one-fifth of it to Pharaoh, and four-fifths will be your own to use for seed for the field and as food for you and those of your households and for your little ones.”

25And they said, “You have saved our lives! Let us find favor in the sight of my lord, and we will be Pharaoh’s servants.”

26And Joseph made it a law over the land of Egypt—valid to this day—that Pharaoh should have the fifth part [of the crops]; only the land of the priests did not become Pharaoh’s.