@BowsacNoodle @Frondeur @Xenophon @blankdeblank @Will2Power If memory serves me (mostly Unbiased Byzantium), the Arians aided the Sassanids since they were opposed to the Church in Constantinople, and on your mention of geography, were principally in Syria, Egypt, and surrounding territories.

You'd need a text on the Muslim conquests through Syria and North Africa to be sure, but it wouldn't surprise me since the Islamic conquests came quickly after the Sassanids fell, and Byzantium was still rebuilding and probably had little opportunity for reprisal against the treasonous Arians.