Question

The 3 cases of nabr in special words are because there is an alif at the end of a word that indicates two and when reading through that alif has to be dropped because of a following sukoon so an accent is there to indicate that dropped alif; if that is right so far then my question is: it seems that there are other places in the Qur'an where there is such an alif followed by a letter with sukoon.  I'm just wondering why these or at least this one here the word     is not included.  Would it simply be because it is a command form of the verb?  Jazakum Allahu khairan

Answer

Wa iyyakum wa-l muslimeen.  Masha’ Allah this is a good question.  Yes the accent or  in the cases of special words is present to indicate that the alif of two doers of the verb was dropped in pronunciation, so not to confuse it with the single past tense of the same verb.  All three places where this reason for nabr are employed are in past tense two person verbs, such as    followed by a sukoon.  If we look at the past tense singular form of    we see it is    .  If the alif for two persons is dropped in pronunciation of  because of a sukoon after, it would then sound exactly like   .  The same does not hold true for the command form.  We do drop the alif for two in pronunciation from the command form verb   when reading in continuum with the next word, because it  starts with a sukoon, but it does not sound like another form of the same verb. The past tense singular form of the verb here would be  and if followed by a sukoon, the last letter   would acquire a kasrah.  
The  in    has a fat-h, there would be no confusion then, and the meaning is understood without any need for a nabr.