Ghunnah on Shadda
Ghunnah on a Shaddah'd Noon or Meem الغُنَّة فِي النُّون وَالمِيم المُشَدَّدَتَيْن
Any noon or meem with shadda is held with a 2-count nasal hum.
A noon or meem carrying shadda is read with a complete ghunnah of two counts. This is the maximum level of ghunnah and the rule applies regardless of vowel or position. Examples: إِنَّ (inna), ثُمَّ (thumma), جَنَّةٌ (jannah).
Quran examples
إِنَّ ٱللَّهَ
Shaddah'd noon — held for 2 counts. · 2:20
مُحَمَّدٌ
Shaddah'd meem — held for 2 counts. · 3:144