Meem Saakin Rules
Idgham Shafawi إِدْغَام شَفَوِيّ
Labial merger — meem saakin + meem.
When meem saakin meets another meem, the two merge into a single meem with shadda, held with a 2-count ghunnah.
Quran examples
لَهُم مَّا
Meem saakin + meem → idgham shafawi. · 2:25