Muslims claim Abraham as their own progenitor, but what then was the religious belief between Abraham and Mohammed for Arabs? Was there some sort of “proto-Islam”? There was a pretty big time gap there, how did the memory of Abraham survive in Arabia without any written texts?
BTW, I’m using the terms “Arab” and “Arabia” because that’s where Islam began, and Mohammed was an Arab, surrounded by Arab traditions.
The most basic answer is that Abraham is a character in the Torah, the five books of the bible now at the core of what is usually called the Old Testament. Judaism established the books as holy; they were then further disseminated by the Christians. While the Arabs until the seventh century had a variety of what we usually now call paganistic religions, they were completely familiar with Judaism and Christianity as primary examples of a monotheistic religion. When Muhammad wanted to disseminate the notion of a single all-powerful god it was both natural and logical to call upon the established religious traditions to give his version historic significance and continuity.
And there were plenty of written texts of the Torah, even though that was not an absolute necessity in an oral culture. While Jews have a long tradition of literacy precisely because of the religious imperative to read the Torah, most Jews and Christians would have large parts, if not the entirety, of the Torah memorized. Memorizing the entirety of the Quran thereafter became a commonplace in the Muslim world.
One mustn’t forget the Arab (and other Middle Eastern) Christians, either. Viewing themselves as part of the seed of Abraham (spiritually speaking), they would’ve kept the Abrahamic saga out front.
So nothing happened between Abraham and Mohammed in the manner that the OP is supposing.
I don’t think we can make that statement, especially not in the five centuries between the fall of Jerusalem and Mohammad.
I will concede it in the case of Jews, though there was considerable concern in that era about this persistence of such teachings, and adoption of non-standard practices and teaching by post-Diaspora communities, leading to the establishment of a system of training rabbis at or by the traditons of certain central scholarly communities [e.g. Caesarea and Tiberias in Palestine (ca. CE 220–375) and Babylonia (ca. CE 200-500] These rabbis and this period in Jewish history is refered to with the word “amoraim”, and this style of torah-based worship is seen as a distinct departure from the Temple based worship that preceded it.
However, in the case of Christianity, there was a definite and immediate departure from the Hebrew language texts and traditions. By CE 100, Christianity was almost entirely practiced outside of the holy land [e.g. Europe and the Near East] using Greek texts – even the Old Testament versions used were translations into the Greek. This caused some serious doctrinal issues in later centuries, as the religion spread and re-encountered those with a knowledge of Hebrew and related tongues, customs and cultures of the Holy Land, which was often very different than the impression common among the Christian communities. You see this addressed in the debates and letters of the Council of Nicaea (CE 325) and later councils, and it was certainly still an issue well-known among Arabs in Mohammed’s time, and Muslims today.
One simple example, which I have often mentioned in this forum, is John 3:16, commonly considered the "most quoted verse in Christianity: “For God so loved the world that He gave his only begotten son…” Any good annotated Bible or translator’s notes will indicate that the word “begotten” does not appear in any of the source texts. In the time/place of Jesus and his disciples, the Hebrew term “bene elohim” (‘son of god’) meant a godly, noble or wise man (as opposed to “bene adam” -‘son of man’- or a common, wordly man) Christianity was based on Greek/Roman/European texts and interpretations (I’ll include Constantiople constellation) for so long that there was little question what “son of God” meant, but the Arabs and other related cultures were equally certain that they knew what it mean, because they were familiar with Hebrew and the related Arab usages and customs, which had not changed in the intervening centuries, and the Hebrew Old Testament, which calls many other great men “bene elohim”. Hence the addition of the extraneous “begotten” to “fix” the problem.
I’m not making a doctrinal point, or claims about the religion. I’m simply noting that texts and language were a stumbling block [translations always are] in early Christianity After the first century AD, they were not nearly as familiar with Hebrew teachings as we might presume today; indeed, thery were not even as familiar with the basic Jewish texts, teachings, and practices as we are. For example, there has been considerable scholarly discussion that a great deal of the New Testament accounts of Jesus’ life and crucifixion was simplified to convey Christian doctrine to communities with no knowledge or interest in the factional politics of Judaism in Jesus’ time [Jesus was a Jew immersed in a Jewish community, but early Christianity distanced itself from that tradition and treated it as “other”]
I think there’s a pretty simple answer to the OP:
Some Arabs were idol worshippers/animists, some were Jews and some were Christians. There was no “proto-Islam” per se; that begins with Mohommed.