Rule: Idgham (with or without ghunnah) only occurs when the noon sakinah is at the end of one word and the merging letter starts the next word.
If they meet within
one word →
obligatory Izhar (Absolute Izhar).
Reason: If merged, the word would be confused with a doubled root.
Four Qur'anic occurrences:
- الدُّنْيَا (115 times) — noon + ya in one word
- بُنْيَانٌ (Saff 4, Tawbah 109-110) — noon + ya
- صِنْوَانٌ (Ra'd 4) — noon + waw
- قِنْوَانٌ (An'am 99) — noon + waw
Al-Jamzouri (Tuhfa v.23): "Unless they meet in one word — do not merge, like Dunya then Sinwan follows."
Question: Why is the noon in "الدُّنْيَا" pronounced clearly even though Ya is among Idgham-with-Ghunnah letters? What are the four cases?
Answer: Because Idgham requires the two letters to be in two separate words. When in one word, Izhar is mandatory. The four cases: Dunya, Bunyan, Sinwan, Qinwan