Supplication for one who fears the injustice of a ruler

"O Allah, Lord of the seven heavens and Lord of the Mighty Throne! Be a protector for me against so-and-so, the son of so-and-so, and his allies from among Your creation — so that none of them may rush upon me or transgress. Mighty is the one under Your protection, great is Your praise, and there is no god but You."

[Sahih al-Adab al-Mufrad 545]