When fearing a person or when one is terrified of a person, one should recite:
اَللَّهُمَّ اكْفِنَاهُ بِمَا شِئْتَ
Trans: O Allah, grant us safety against him as, and how you please.
The author states that this hadith is authentic and Abu Nu’aim has mentioned it in his book al-Mustakhraj ala Sahih Muslim.
Source: al-Hisnul Haseen by Allamah Muhammad al-Jazri Rahimullah