Complex sentence: He is reported as doing this by claiming biological descent from Abraham through his slave wife Hagar for the Arabs in the same way as the Jews who claimed descent from Abraham through Sarah and thus as their ancestral faith.
Split into simpler sentences: He is reported as doing this by claiming biological descent from Abraham through his slave wife Hagar for the Arabs. This united the ancestors of the tribe with the religion, in the same way as the Jews claimed descent from Abraham through Sarah and their ancestral faith.