Genesis 47:22-26

Only the land of the priests he did not buy, because the priests had an allotment from Pharaoh, and they lived off the allotment which Pharaoh gave them. Therefore, they did not sell their land.

Then Joseph said to the people, “Behold, today I have purchased you and your land for Pharaoh; now, here is seed for you, and you may sow the land.

At the harvest you shall give a fifth to Pharaoh, and four-fifths shall be your own for seed of the field and for your food, and for those of your households and as food for your little ones.”

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

Joseph made it a statute concerning the land of Egypt, valid to this day, that Pharaoh was to have the fifth; only the land of the priests did not become Pharaoh’s.