Genesis 47:24-26 New International Version - UK (NIVUK)
24 But when the crop comes in, give a fifth of it to Pharaoh. The other four-fifths you may keep as seed for the fields and as food for yourselves and your households and your children.’
25 ‘You have saved our lives,’ they said. ‘May we find favour in the eyes of our lord; we will be in bondage to Pharaoh.’
26 So Joseph established it as a law concerning land in Egypt – still in force today – that a fifth of the produce belongs to Pharaoh. It was only the land of the priests that did not become Pharaoh’s.