Looking at old German orthographies, the long-s (ſ) spelling of the following five words (and I have not found any others so far) contradicts the spelling systematics of all other words:
Iſrael, Iſlam, Moſlem, Iſmael, Aſbeſt
Broken down to what matters for these words, a long s would only be consistent with the spelling systematics, if it were at the beginning of a syllable. While this is the case for none of these words in their German pronunciation, I can at least explain the spelling of Aſbeſt to some extent: It originates from the Greek ἄ-σβεστος and thus the first s was at the beginning of a syllable or word part etymologically (the second long s is consistent anyway, since it is followed by a t). I now wonder whether there is a similar explanation for the other words.
Is there any etymological predecessor for any of the words Israel, Islam, Moslem (muslim) and Ismael (Ishmael), in which the s (or a corresponding sound) was at the beginning of a syllable
or word part?
Thanks to the comments and answers so far, I looked into Semitic morphology and understood that the concept of discrete word parts cannot be applied here. Still, my question about syllables stands, since they are relevant for long-s spelling, regardless of the underlying morphology.
Also, I looked for other words of Semitic origin (and with an s in a comparable position), and found only Kismet and Esra, both spelt without a long s.