וַיָּ֣שֶׂם אֹתָ֣הּ יוֹסֵ֡ף לְחֹק֩ עַד־הַיּ֨וֹם הַזֶּ֜ה עַל־אַדְמַ֥ת מִצְרַ֛יִם לְפַרְעֹ֖ה לַחֹ֑מֶשׁ רַ֞ק אַדְמַ֤ת הַכֹּֽהֲנִים֙ לְבַדָּ֔ם לֹ֥א הָיְתָ֖ה לְפַרְעֹֽה׃
And Joseph made it a statute concerning the land of Egypt unto this day, that Pharaoh should have the fifth; only the land of the priests alone became not Pharaoh’s.
Read kabbalistic (mystical) interpretation of Genesis 47:26: and classical mystical sources.