As-salaam Alaykum brothers and sisters in Islam. Where in the Quran is the 4 exceptions of Idgaam? Where Idgaam rules will not be apply.
May Almighty Allah grant you more wisdom.
Wa Alaikum Assalam Wa Rahmatullahi Wa Barakatuh,
The exception to the rules of Idghaam can be found in the following lessons:
http://www.abouttajweed.com/the-noon-saakinah-and-tanween/merging-of-the-noon-saakinah-and-tanween-p.html (end of page)
Ameen to your dua'. May Allah bless you and all the muslims. Ameen.