Al-Mundhiri recorded the following chapter in his book Al-Targhib wal-Tarhib:

التَّرْغِيب فِي كَلِمَات يقولهن من خَافَ ظَالِما

Encouragement for words to say when fearing an oppressor.

Source: al-Targhīb wal-Tarhīb 3/133

Sa’id ibn Jubayr reported: Ibn Abbas, may Allah be pleased with him, said:

إِذَا أَتَيْتَ سُلْطَانًا مَهِيبًا تَخَافُ أَنْ يَسْطُوَ عَلَيْكَ فَقُلْ اللَّهُ أَكْبَرُ اللَّهُ أَعَزُّ مِنْ خَلْقِهِ جَمِيعًا اللَّهُ أَعَزُّ مِمَّا أَخَافُ وَأَحْذَرُ أَعُوذُ بِاللَّهِ الَّذِي لَا إِلَهَ إِلَّا هُوَ الْمُمْسِكُ السَّمَاوَاتِ السَّبْعِ أَنْ يَقَعْنَ عَلَى الْأَرْضِ إِلَّا بِإِذْنِهِ مِنْ شَرِّ عَبْدِكَ فُلَانٍ وَجُنُودِهِ وَأَتْبَاعِهِ وَأَشْيَاعِهِ مِنَ الْجِنِّ وَالْإِنْسِ اللَّهُمَّ كُنْ لِي جَارًا مِنْ شَرِّهِمْ جَلَّ ثَنَاؤُكَ وَعَزَّ جَارُكَ وَتَبَارَكَ اسْمُكَ وَلَا إِلَهَ غَيْرُكَ ثَلَاثَ مَرَّاتٍ

If an imposing ruler comes to you and you fear he will pillage you, then say three times: Allah is the greatest, Allah is more powerful than all His creation together, Allah is mightier than what I fear and worry. I seek refuge in Allah, there is no God but Him, the Holder of the seven heavens lest they fall upon the earth but by His permission, from the evil of Your servant this man, his soldiers, his followers, and his partisans among jinn and humanity. O Allah, be my protector from his evil, for majestic is Your praise, mighty is Your protection, and blessed is Your name. There is no God besides You.

Source: Muṣannaf Ibn Abī Shaybah 29177, Grade: Sahih

Al-Harith ibn Suwayd reported: Abdullah ibn Mas’ud, may Allah be pleased with him, said:

إِذَا كَانَ عَلَى أَحَدِكُمْ إِمَامٌ يَخَافُ تَغَطْرُسَهُ أَوْ ظُلْمَهُ فَلْيَقُلِ اللَّهُمَّ رَبَّ السَّمَاوَاتِ السَّبْعِ وَرَبَّ الْعَرْشِ الْعَظِيمِ كُنْ لِي جَارًا مِنْ فُلَانِ بْنِ فُلَانٍ وَأَحْزَابِهِ مِنْ خَلَائِقِكَ أَنْ يَفْرُطَ عَلَيَّ أَحَدٌ مِنْهُمْ أَوْ يَطْغَى عَزَّ جَارُكَ وَجَلَّ ثَنَاؤُكَ وَلَا إِلَهَ إِلَّا أَنْتَ

If a leader is appointed over you from whom you fear arrogance or injustice, let him say: O Allah, Lord of the seven heavens, Lord of the Mighty Throne, be my protector against this man, the son of this man, and his partisans among Your creatures, lest one of them transgress against me or oppress me. Powerful is Your protection and majestic is Your praise, for there is no God but You.

Source: al-Adab al-Mufrad lil-Bukhārī 707, Grade: Sahih