On Wed, 29 Jun 2005, Gregg Reynolds wrote:
Even then, Arabic script does not fully cover the Arabic language from a linguistic perspective. A (or maybe /the/) striking example is the inserted vowel between the /n/ of tanween and any initial cluster of consonants, e.g., /muHammadu-ni r-rasuulu/: it has no orthographic expression (I found it described as kasra, bound to a small nuun in an Ottoman handbook, but I never attested it in a manuscript).
(I think you mean /muHammadu-nu r-rasuulu/ ;)