القرآن شفاء عام
The Qur'an's own description of itself as a source of healing — the foundation Ibn al-Qayyim builds on before discussing any specific ruqyah or physical remedy.
وَنُنَزِّلُ مِنَ الْقُرْآنِ مَا هُوَ شِفَاءٌ وَرَحْمَةٌ لِلْمُؤْمِنِينَ
“And We send down of the Qur'an that which is a healing and a mercy for the believers.” (meaning, not a literal translation)
Distinct from the specific narrated incident behind the existing 'Ruqyah with Surah al-Fatiha' entry — this verse is the general principle those specific narrations are built on.
Ibn al-Qayyim opens the spiritual-medicine section of Zad al-Ma'ad by arguing the Qur'an is the most complete cure available, addressing diseases of the heart first and, by Allah's permission, the body as well.