Meem Saakin Rules
Ikhfa Shafawi إِخْفَاء شَفَوِيّ
Lip concealment — meem saakin + ba.
When meem saakin is followed by ba, the lips close lightly on the meem with a 2-count ghunnah, then open into the ba. The two letters share the same articulation point (both lips), making this a "labial concealment."
Quran examples
هُم بِالْآخِرَةِ
Meem saakin + ba → ikhfa shafawi. · 2:4