...What we have settled on and determined to be certain is that Syriac and Hebrew and Arabic - that is the language of Mudar and Rabia (ie Arabic as we know it), not the language of Himyar (ie Old South Arabian) - are one language that changed with the migrations of its people, so that it was ground up... For, when a town's people live near another people, their language changes in a manner clear to anyone who considers the issue, and we find that the masses have changed the pronunciation of Arabic significantly, to the point that it is so distant from the original as to be like a different language, so we find them saying `iinab for `inab (grape), and 'asTuuT for sawT (whip), and thalathdaa for thalaathatu danaaniir (three dinars), and when a Berber becomes Arabized and wants to say shajarah (tree) he says sajarah, and when a Galician becomes Arabized he replaces `ayn and Haa with haa, so he says muhammad when he means to say muHammad, and such things are frequent. So whoever ponders on Arabic, Hebrew, and Syriac will become certain that their difference is of the type we have described, through changes in people's pronunciation through the passage of time and the difference of countries and the bordering of other nations, and that they are in origin a single language. Having established that, Syriac is the ancestor of both Arabic and Hebrew, and to be more precise, the first to speak this Arabic was Ishmael, upon him be peace, for it is the language of his sons, and Hebrew is the language of Isaac and his sons, and Syriac is without doubt the language of Abraham, blessings and peace be upon him and upon our prophet. (Ihkam Ibn Hazm; see Wikisource for original text, beginning الذي وقفنا عليه وعلمناه يقينا أن السريانية والعبرانية والعربية...)
My attention was originally drawn to this remarkable quote by an article by Ahmad Shahlan, in a rather strange Libyan book fusing pan-Arab nationalism with Semitic philology, at-Tanawwu` wal-Wahdah fi l-lahajaati l-`uruubiyyati l-qadiimati, which probably merits a post in its own right at some point.