I have a question about the rule of what to do when two saakin letters meet.

Question
Assalaamu alaykum

I have a question about the rule of what to do when two saakin letters meet. I understand that when joining verse 1 and 2 of suratul Ale Imran the meem acquires a fathah. But I cannot find it explained in the rules for two saakin letters meeting. Is this the exception. If so where else is this applied and why?

May Allah multiply your good deeds and increase the team with more blessed knowledge.

Jazak Allahu Khayran

Assalaamu alaykum

Answer
Wa alaikum assalaam wa rahmatullahi wa barakaatuh

This is a special case and does not follow any rule of the rules for the normal occurrence of two saakin letters meeting.  The reason is that this is not the plural meem (), instead this is a separate letter of the separate letters which occur at the beginning of some surahs.  In this case the obtains a fathah when joining it with the beginning of the next aayah.
The medd laazim harfi then, when joining the two aayaat, can be lengthened either 6 counts, based on it being a permanent sukoon which acquired a vowel, or it can be lengthened two vowel counts since a temporary vowel has been put on the last . 
Please also see:
http://www.abouttajweed.com/kb/entry/549/

Wa iyyaakum
Wa assalaam alaikum wa rahmatullahi wa barakaath