Shari'ah a.s.o.

At first Mohammad believed that both Jews and Christians would welcome him. It is only later, when he realized that he could never gain support from either of them, that he presented Islam as a new faith. He accepted whatever of their traditions that came within the purview of his plan, making such changes as he saw fit. This accounts for the seeming discrepancies between the stories of the Bible and the Koranic version of the same narratives. However, in relating the Koranic version of the biblical story to the Aggadic source as indicated before, the discrepancies almost entirely disappear. For, astonishingly enough, the biblical narratives are reproduced in the Koran in true Aggadic cloak.

At the time of Mohammad's appearance, a great number of Jews made their home in Arabia, where, indeed, they had lived for many centuries.
The Hebrew Bible contains a number of references to the close relationship between Arabs and Jews. Commercial relations on a large scale between Palestine and Arabia certainly go back to the days of Solomon; and many books of the Old Testament, particularly Job and Proverbs, which arevstrongly marked by the presence of Arabic words, show the connection was steadily maintained. We may gather that the Arab Jews possibly exercised a certain indirect influence on the construction of the a Talmud. Some paragraphs in the Misnah refer exclusively to the Jews of the Peninsula. It was considered lawful for them to live in Bedouin tents, and their women were permitted to go out on Sabbath wearing a veil. The Talmud also alludes to the custom of circumcision among Arabs and twice mentions Arab foot-gear.

Arabic sources abound in incidents attesting to the friendly relations between the Jews and the Arabs in the pre-Islamic period (Jahiliyah).
The southern part of the Arabian peninsula, known as Yemen, was generally considered a Jewish state. The last Himyar king, Dhu Nuwas,
who converted to Judaism, fell in battle in 525 C.E. The Jews of Yemen wrought a tremendous change in the religious life of the Arab people, hundreds of years before the advent of Muhammad. It is likely that had the Islam not appeared, the Jews and the Christians would have absorbed all Arabia into their faiths.

The Arab tribes in the Yahiliyah period who had accepted Judaism followed Jewish practices extensively. Jewish customs and traditions were known to and practiced by many Arabs, and Muhammad who knew many of these laws and customs incorporated a considerable number of them into his religious teachings. In fact I would not know of a main Islamic idea that did not come from Christians and Jews, except for the Shari'ah a.s.o.: later additions & some strange Arab superstitions (all religions change & "adjust" rules) ...