Question

Assalaamu alaikum to you and Allah's blessings.

We have a question which one student was asking in our tajweed class; we were wondering if, insha Allah, you could help us out as we don't know the answer.

She was asking why the wow maddiyyah followed by a regular wow (ghair maddiyya) with a vowel on it or a ya' maddiyya followed by a regular unlengthened ya' (ghair maddiyya) with a vowel on it were cited as exceptions to the idgham sagheer mutamathilain when they aren't mutamathilaan?

As for ex. in this aayah from surah Al Bayyinah:

We are grateful to be able to address our questions to you and pray that Allah reward you.

Answer

Wa alaikum assalaam wa rahmatu Allahi wa barakatuh.

There is a difference of opinion among scholars about the articulation point of the lengthened letters  and .  Some scholars say they come from the empty part of the throat and mouth () exclusively, others say that the lengthened  or wow meddiyyah, comes from the same articulation point as the unlengthened wow, which is the two lips; and that the lengthened  comes from the same articulation point as the unlengthened ya', which is the middle of the tongue and that which lies opposite to it from the roof of the mouth. 

 A third group say that the  meddiyyah, or lengthened wow, uses both the empty space in the throat and mouth (is articulated by vibration of the vocal chords) and this is accompanied by a circling of the two lips, which of course, is the articulation point of the non-lengthened.  If you attempt to say the lengthened  in the example in your question,  without using your two lips, you will not end up with a proper letter.  It is very necessary to use the two lips in conjunction with the vibration of the vocal chords (using empty space in throat and mouth).  

You can then see that the two lips are used in both the unlengthened  and lengthened, so it is not possible to say that they come from two different articulation points and therefore are not mutamaathilayn ().  This is the school of thought that his eminence Ash-Sheikh Dr. Ayman Swayd adheres to, and the one that clears up any doubts anyone may have about the exception of the lengthened  and  to the idghaam mutamaathilayn.  What is said about the lengthened  can be said about the lengthened.  And Allah knows best.