What from the Qur’an or adhkar should we recite to ward off the harm of a Christian sorcerer and his black cats, and to avoid their evil?

It is recommended to be keen on guiding Christians to Islam, for the Messenger of Allah, peace and blessings be upon him, said: "For Allah to guide a single man through you is better for you than red camels." To guard against magic and harm, it is recommended to maintain the morning and evening remembrances (adhkar), ask Allah for well-being, and frequently recite the Qur’an, especially Surah Al-Ikhlas and the two Mu'awwidhat (Surah Al-Falaq and Surah An-Nas) three times in the morning and evening, because the Prophet, peace and blessings be upon him, said: "Say 'Qul Huwa Allahu Ahad' and the two Mu'awwidhat when you enter the evening and when you enter the morning, three times, they will suffice you against everything." When fearing a people, one should say: "O Allah, we place You before them and we seek refuge in You from their evils." It is also recommended to repeat "Hasbi Allahu la ilaha illa Huwa, 'alayhi tawakkaltu wa Huwa Rabbu al-'Arshil-'Atheem" (Allah suffices me, there is no god but He; in Him I put my trust, and He is the Lord of the Mighty Throne) seven times in the morning and evening, and to say: "Bismillahil-ladhi la yadurru ma'asmihi shay'un fil-ardi wa la fis-sama'i wa Huwas-Sami'ul-'Aleem" (In the Name of Allah with Whose Name nothing on earth or in the heavens can cause harm, and He is the All-Hearing, the All-Knowing) three times in the morning and evening.